Update DIMM memorySizeInKB to be in size_t

Following the changes in
https://gerrit.openbmc.org/c/openbmc/phosphor-dbus-interfaces/+/41870
where `MemorySizeInKB` type changed from `uint32` to `size`.

Tested:
On a 64-bit system, MemorySizeInKB has type `t`, which is uint64.
```
.MemorySizeInKB                         property  t         33554432                                 emits-change writable
```
Before:
```
[ERROR "dbus_utils.hpp":21] DBUS property error in property: MemorySizeInKB, reason: 1
---
~# curl localhost/redfish/v1/Systems/system -s \
  | grep -A7 MemorySummary
  "MemorySummary": {
    "Status": {
      "Health": "OK",
      "HealthRollup": "OK",
      "State": "Disabled"
    },
    "TotalSystemMemoryGiB": 0
  },
```
After:
```
~# curl localhost/redfish/v1/Systems/system -s \
  | grep -A7 MemorySummary
  "MemorySummary": {
    "Status": {
      "Health": "OK",
      "HealthRollup": "OK",
      "State": "Enabled"
    },
    "TotalSystemMemoryGiB": 64
  },
```

Change-Id: Ifc66d4cf78ea81629957091bc4f3b407aa96355a
Signed-off-by: Anthony <anthonyhkf@google.com>
diff --git a/redfish-core/lib/systems.hpp b/redfish-core/lib/systems.hpp
index 1cedf2d..b051899 100644
--- a/redfish-core/lib/systems.hpp
+++ b/redfish-core/lib/systems.hpp
@@ -339,7 +339,7 @@
                                 return;
                             }
 
-                            const uint32_t* memorySizeInKB = nullptr;
+                            const size_t* memorySizeInKB = nullptr;
 
                             const bool success =
                                 sdbusplus::unpackPropertiesNoThrow(
@@ -366,14 +366,16 @@
                                     aResp->res
                                         .jsonValue["MemorySummary"]
                                                   ["TotalSystemMemoryGiB"] =
-                                        *memorySizeInKB / (1024 * 1024);
+                                        *memorySizeInKB /
+                                        static_cast<size_t>(1024 * 1024);
                                 }
                                 else
                                 {
                                     aResp->res
                                         .jsonValue["MemorySummary"]
                                                   ["TotalSystemMemoryGiB"] =
-                                        *memorySizeInKB / (1024 * 1024) +
+                                        *memorySizeInKB /
+                                            static_cast<size_t>(1024 * 1024) +
                                         *preValue;
                                 }
                                 aResp->res.jsonValue["MemorySummary"]["Status"]