[media] s5p-mfc: fix typo in s5p_mfc_dec function comment

The function comment has an obvious typo error, so fix it.

Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: Kamil Debski <k.debski@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>