media: v4l2: Fix the _MPLANE format check in v4l_enum_fmt()

CAP_M2M_MPLANE means the device supports _MPLANE formats for both
capture and output. Adjust the check to avoid EINVAL errors on
such devices.

Reported-by: Maxime Jourdan <mjourdan@baylibre.com>
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Tomasz Figa <tfiga@chromium.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>