drm/omap: check return value from soc_device_match

soc_device_match() can return NULL, so add a check and fail if
soc_device_match() fails.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180502091159.7071-2-tomi.valkeinen@ti.com


Reviewed-by: Benoit Parrot <bparrot@ti.com>
Reviewed-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>