[media] s5p-fimc: add unlock on error path

There was an unlock missing if kzalloc() failed.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>