freedreno: Restore msm_drm.h to a pristine "make headers_install" copy.

This diverged back in f1374805a8 ("drm-uapi: use local files, not system
libdrm") to point at drm-uapi's copy, which we don't need now that we're
actually in drm-uapi.

Reviewed-by: Rob Clark <robdclark@gmail.com>

include/drm-uapi/msm_drm.h

@@ -25,7 +25,7 @@
 #ifndef __MSM_DRM_H__
 #define __MSM_DRM_H__
 
-#include "drm-uapi/drm.h"
+#include "drm.h"
 
 #if defined(__cplusplus)
 extern "C" {