V4L/DVB: media/IR/imon: potential double unlock on error

If there is an error here we should unlock in the caller (which is
imon_init_intf1()).  We can remove this stray unlock.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: Jarod Wilson <jarod@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>