[media] s5p-fimc: Fix fimc-lite entities deregistration

Clear the proper array when deregistering FIMC-LITE devices. Now
fimc[] array is erroneously accessed instead of fimc_lite[] and
fimc_md_unregister_entities() function call can result in an oops
from NULL pointer dereference, since fmd->fimc[] is cleared earlier.
This might happen in normal conditions when the driver's probing
is deferred and then retried.

Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>