media: v4l2-core: fix touch support in v4l_g_fmt

v4l_s_fmt, for VFL_TYPE_TOUCH, sets unneeded members of
the v4l2_pix_format structure to default values.This was
missing in v4l_g_fmt, which would lead to failures in
v4l2-compliance tests.

Signed-off-by: Vandana BN <bnvandana@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>