[media] s5p-mfc: fix spelling errors

This patch fixes spelling errors in mfc encoder.
inavild -> invaild

Signed-off-by: Ingi Kim <ingi2.kim@samsung.com>
Signed-off-by: Kamil Debski <k.debski@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>