media: rzv2h-ivc: Fix concurrent buffer list access

media: rzv2h-ivc: Fix concurrent buffer list access

The list of buffers (`rzv2h_ivc::buffers.queue`) is protected by a
spinlock (`rzv2h_ivc::buffers.lock`). However, in
`rzv2h_ivc_transfer_buffer()`, which runs in a separate workqueue, the
`list_del()` call is executed without holding the spinlock, which makes
it possible for the list to be concurrently modified

Fix that by removing a buffer from the list in the lock protected section.

Cc: stable@vger.kernel.org
Fixes: f0b3984d821b ("media: platform: Add Renesas Input Video Control block driver")
Reviewed-by: Daniel Scally <dan.scally@ideasonboard.com>
Signed-off-by: Barnabás Pőcze <barnabas.pocze+renesas@ideasonboard.com>
[assign ivc->buffers.curr in critical section as reported by Barnabas]
Signed-off-by: Jacopo Mondi <jacopo.mondi+renesas@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>