[media] mn88472: Fix possible leak in mn88472_init()

Commit 307e95c9 ("[media] mn88472: implement firmware parity check")
introduced the usage of exit paths that do not free the already allocated
firmware data in case the parity handling fails. Go through the correct
exit paths. Detected by Coverity CID 1295989.

Signed-off-by: Christian Engelmayer <cengelma@gmx.at>
Acked-by: Benjamin Larsson <benjamin@southpole.se>
Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>