media: hantro: Use output buffer width and height for H264 decoding

Calculations for motion vector buffer offset is based on width and height
from the configured output format, lets use the same values for macroblock
width and height hw regs.

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>