[media] mn88473: One function call less in mn88473_init() after error

The release_firmware() function was called by the mn88473_init() function even
if a previous function call "request_firmware" failed.
This implementation detail could be improved by the introduction of another
jump label.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>