Before reading which slot was captured to by examining the module status
(VnMS) register, make sure something was captured at all by examining
the interrupt status register (VnINTS).

Failing this a buffer maybe completed before it was captured too.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>