ArmPkg/MmCommunicationDxe: fix logic bug in DXE driver entrypoint

Commit 2fe25a74d6 ("ArmPkg/MmCommunicationDxe: relay architected PI
events to MM context") update the ARM specific standalone MM client
driver to register for certain events in the entrypoint code, but did
so in a way that makes the entrypoint always return with an error.

Instead, return EFI_SUCCESS if registering for those events succeeds,
and back out the registrations that did succeed if one fails, and
return an error.

Fixes: 2fe25a74d6 ("ArmPkg/MmCommunicationDxe: relay architected PI events to MM context")
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif@nuviainc.com>

ArmPkg/Drivers/MmCommunicationDxe/MmCommunication.c

@@ -390,8 +390,16 @@ MmCommunicationInitialize (
                     MmGuidedEventNotify, mGuidedEventGuid[Index],
                     mGuidedEventGuid[Index], &mGuidedEvent[Index]);
     ASSERT_EFI_ERROR (Status);
+    if (EFI_ERROR (Status)) {
+      while (Index-- > 0) {
+        gBS->CloseEvent (mGuidedEvent[Index]);
+      }
+      goto UninstallProtocol;
+    }
   }
+  return EFI_SUCCESS;
 
+UninstallProtocol:
   gBS->UninstallProtocolInterface (
          mMmCommunicateHandle,
          &gEfiMmCommunicationProtocolGuid,