drm: Fix typo in vmwgfx_drv.c

Correct spelling "unsuported" to "unsupported" in
drivers/gpu/drm/vmwgfx/vmwgfx_drv.c

Signed-off-by: Masanari Iida <standby24x7@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>