[media] s5p_mfc: use static for some structs

drivers/media/platform/s5p-mfc/s5p_mfc.c:1334:28: warning: symbol 'mfc_buf_size_v5' was not declared. Should it be static?
drivers/media/platform/s5p-mfc/s5p_mfc.c:1341:25: warning: symbol 'buf_size_v5' was not declared. Should it be static?
drivers/media/platform/s5p-mfc/s5p_mfc.c:1347:26: warning: symbol 'mfc_buf_align_v5' was not declared. Should it be static?
drivers/media/platform/s5p-mfc/s5p_mfc.c:1360:28: warning: symbol 'mfc_buf_size_v6' was not declared. Should it be static?
drivers/media/platform/s5p-mfc/s5p_mfc.c:1368:25: warning: symbol 'buf_size_v6' was not declared. Should it be static?
drivers/media/platform/s5p-mfc/s5p_mfc.c:1374:26: warning: symbol 'mfc_buf_align_v6' was not declared. Should it be static?
drivers/media/platform/s5p-mfc/s5p_mfc.c:1392:28: warning: symbol 'mfc_buf_size_v7' was not declared. Should it be static?
drivers/media/platform/s5p-mfc/s5p_mfc.c:1400:25: warning: symbol 'buf_size_v7' was not declared. Should it be static?
drivers/media/platform/s5p-mfc/s5p_mfc.c:1406:26: warning: symbol 'mfc_buf_align_v7' was not declared. Should it be static?
drivers/media/platform/s5p-mfc/s5p_mfc.c:1419:28: warning: symbol 'mfc_buf_size_v8' was not declared. Should it be static?
drivers/media/platform/s5p-mfc/s5p_mfc.c:1427:25: warning: symbol 'buf_size_v8' was not declared. Should it be static?
drivers/media/platform/s5p-mfc/s5p_mfc.c:1433:26: warning: symbol 'mfc_buf_align_v8' was not declared. Should it be static?

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>