media: media/pci/ivtv: Variable vbi.type could be uninitialized if macro v4l2_subdev_call set __result an error code

Inside function compress_sliced_buf(), variable vbi.type is
uninitialized if macro v4l2_subdev_call set __result an
error code. However, vbi.type is used in the if statement
without any check, which is potentially unsafe.
Signed-off-by: Yizhuo <yzhai003@ucr.edu>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>