drm: shmobile: fix warnings

drivers/gpu/drm/shmobile/shmob_drm_drv.c:300:5: warning: "CONFIG_PM_SLEEP" is not defined [-Wundef]

Always use #ifdef with CONFIG symbols, never just bare #if

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Dave Airlie <airlied@redhat.com>