re: media: rcar-vin: add group allocator functions

[Colin Ian King]

Hi there,

While running static analysis on linux-next today a null pointer
dereference issue was detected by CoverityScan. The following commit
introduced the issue:

commit 3bb4c3bc85bf77a76c921671800bde2e1bf82a88
Author: Niklas SÃderlund <niklas.soderlund+renesas@xxxxxxxxxxxx>
Date:   Sat Apr 14 07:57:18 2018 -0400

    media: rcar-vin: add group allocator functions

The analysis is as follows:

339 static void rvin_group_put(struct rvin_dev *vin)
340 {
341        mutex_lock(&vin->group->lock);
342
   1. assign_zero: Assigning: vin->group = NULL.

343        vin->group = NULL;
344        vin->v4l2_dev.mdev = NULL;
345
    CID 1468359 (#1 of 1): Explicit null dereferenced (FORWARD_NULL)
    2. var_deref_op: Dereferencing null pointer vin->group.

346        if (WARN_ON(vin->group->vin[vin->id] != vin))
347                goto out;
348

vin->group is NULL however the WARN_ON is dereferencing it, causing an
OOPS.  I don't know how this should be fixed, hence I am sending this
bug report.

Regards,

Colin