memory: correct type of MemorySizeInKB

This is needed for this code to work on both 32 and 64 bits system.
According to the interface,
https://github.com/openbmc/phosphor-dbus-interfaces/blob/388b58f9a878f45b8ec243152cac5eb44ec90ced/yaml/xyz/openbmc_project/Inventory/Item/Dimm.interface.yaml#L9,
MemorySizeInKB is of type size_t.

Tested:
On real hardware, the memory resource is working as expected.

Signed-off-by: Nan Zhou <nanzhoumails@gmail.com>
Change-Id: Ie81d2610c245a08a22c3ea891495f34cc0bdc075
diff --git a/redfish-core/lib/memory.hpp b/redfish-core/lib/memory.hpp
index 20bbfb2..6e4ab67 100644
--- a/redfish-core/lib/memory.hpp
+++ b/redfish-core/lib/memory.hpp
@@ -465,8 +465,8 @@
                 }
                 else if (property.first == "MemorySizeInKB")
                 {
-                    const uint32_t* memorySize =
-                        std::get_if<uint32_t>(&property.second);
+                    const size_t* memorySize =
+                        std::get_if<size_t>(&property.second);
                     if (memorySize == nullptr)
                     {
                         // Important property not in desired type