[media] s3c-camif: forever loop in camif_hw_set_source_format()

Because "i" is unsigned then "i-- >= 0" is always true.  If we don't
find what we are looking for then we loop forever.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>