ArmPkg: Fix Ecc error 8005 for SCMI_STATUS

This patch fixes the following Ecc reported error:
Variable name does not follow the rules:
1. First character should be upper case
2. Must contain lower case characters
3. No white space characters
4. Global variable name must start with a 'g'

Signed-off-by: Pierre Gondois <Pierre.Gondois@arm.com>
Reviewed-by: Sami Mujawar <sami.mujawar@arm.com>

ArmPkg/Drivers/ArmScmiDxe/Scmi.c

@@ -123,7 +123,7 @@ ScmiCommandExecute (
 
   Response = (SCMI_MESSAGE_RESPONSE*)MtlGetChannelPayload (Channel);
 
-  if (Response->Status != SCMI_SUCCESS) {
+  if (Response->Status != ScmiSuccess) {
     DEBUG ((DEBUG_ERROR, "SCMI error: ProtocolId = 0x%x, MessageId = 0x%x, error = %d\n",
       Command->ProtocolId,
       Command->MessageId,