video: mmp: fix graphics/video layer enable/mask swap issue

There is bug when switch dma of graphic layer and video layer, it
configured opposite bit, fix it.

Signed-off-by: Jing Xiang <jxiang@marvell.com>
Signed-off-by: Jett.Zhou <jtzhou@marvell.com>
Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>