[media] staging: media: go7007: firmware protection Protection for unfirmware load

If no firmware was loaded (no exists,wrong or some error) then rmmod
fails with OOPS, so need some protection stuff.

Signed-off-by: Volokh Konstantin <volokh84@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>