ArmPkg: Fix Ecc error 8005 for SCMI_MESSAGE_TYPE

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

@@ -95,7 +95,7 @@ ScmiCommandExecute (
   // Fill in message header.
   MessageHeader = SCMI_MESSAGE_HEADER (
                     Command->MessageId,
-                    SCMI_MESSAGE_TYPE_COMMAND,
+                    ScmiMessageTypeCommand,
                     Command->ProtocolId
                     );