drm/amd/powerplay: rename smum header guards

This patch renames the smum header guards to align with the file name.
Reported-by: Edward O'Callaghan <funfunctor@folklore1984.net>
Signed-off-by: Huang Rui <ray.huang@amd.com>
Reviewed-by: Ken Wang <Qingqing.Wang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/iceland_smum.h

@@ -21,8 +21,8 @@
  *
  */
 
-#ifndef ICELAND_SMUMGR_H
-#define ICELAND_SMUMGR_H
+#ifndef ICELAND_SMUM_H
+#define ICELAND_SMUM_H
 
 #include "ppsmc.h"