i2c-vr: use hexadecimal format for version instead of decimal

Testd on Harma:
```
 curl --silent $creds https://$bmc/redfish/v1/UpdateService/FirmwareInventory/Harma_MB_VR_cpu0_pvdd11_7313
```
```
{
  "@odata.id": "/redfish/v1/UpdateService/FirmwareInventory/Harma_MB_VR_cpu0_pvdd11_7313",
  "@odata.type": "#SoftwareInventory.v1_1_0.SoftwareInventory",
  "Description": "Unknown image",
  "Id": "Harma_MB_VR_cpu0_pvdd11_7313",
  "Name": "Software Inventory",
  "Status": {
    "Health": "Warning",
    "HealthRollup": "OK",
    "State": "Disabled"
  },
  "Updateable": true,
  "Version": "EA79EAEE"
}
```

Change-Id: Ic7aa4216b8b27159a76af0c5116b784543c1f46b
Signed-off-by: Kevin Tung <kevin.wtmh@gmail.com>
diff --git a/i2c-vr/i2cvr_software_manager.cpp b/i2c-vr/i2cvr_software_manager.cpp
index 2c85da8..f1df77b 100644
--- a/i2c-vr/i2cvr_software_manager.cpp
+++ b/i2c-vr/i2cvr_software_manager.cpp
@@ -88,7 +88,7 @@
         co_return false;
     }
 
-    software->setVersion(std::to_string(sum));
+    software->setVersion(std::format("{:X}", sum));
 
     std::set<RequestedApplyTimes> allowedApplyTime = {
         RequestedApplyTimes::Immediate, RequestedApplyTimes::OnReset};