drm/vmwgfx: Fix drm.h include

The userspace drm.h include doesn't prefix the drm directory.  This can lead
to compile failures as /usr/include/drm/ isn't in the standard gcc include
paths.  Fix it to be <drm/drm.h>, which matches the rest of the driver drm
header files that get installed into /usr/include/drm.

Red Hat Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1138759



Fixes: 1d7a5cbf
Reported-by: Jeffrey Bastian <jbastian@redhat.com>
Signed-off-by: Josh Boyer <jwboyer@fedoraproject.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>