media: ti-vpe: cal: remove unneeded assignment

v4l2_fill_pix_format() already copies mbus_fmt.field, so no need to do
it again.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>