[media] mn88472: One function call less in mn88472_init() after error detection

The release_firmware() function was called in three cases by the mn88472_init()
function during error handling even if the passed variable "fw" contained still
a null pointer.

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>