Fix loop filtering bug in non-420 video.

BUG=aomedia:386

Fix the bug by separating mask_4x4_int into mask_4x4_int_r and
mask_4x4_int_c. The horizontal and vertical filtering are now
correctly handled.

Change-Id: I2207a12c83cba3e3003e1e45c7587695ad87a691
1 file changed