[media] av7110: fix sparse warning

drivers/media/pci/ttpci/av7110.c:1226:15: warning: memset with byte count of 192512

Instead of memsetting this in one go, loop over each line and memset each line
separately.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>