[media] s5p-mfc: Update scratch buffer size for MPEG4

Update the MPEG4 decoder scratch buffer size as per the
new v6 firmware. This updation is increasing the size and so
is backward compatible with older v6 firmwares.

Signed-off-by: Arun Kumar K <arun.kk@samsung.com>
Signed-off-by: Kamil Debski <k.debski@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>