video: metronomefb: add __devexit_p around reference to metronomefb_remove

metronomefb_remove is marked __devexit,
thus add __devexit_p around reference to metronomefb_remove.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>