[media] s5p-mfc: fix a typo in s5p_mfc_dec

It is a cosmetic commit.

Signed-off-by: ayaka <ayaka@soulik.info>
Signed-off-by: Kamil Debski <k.debski@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>