bridge: Use PTR_ERR_OR_ZERO instead if(IS_ERR(...)) + PTR_ERR

coccicheck suggested using PTR_ERR_OR_ZERO() and looking at the code.

Fix the following coccicheck warnings:

./net/bridge/br_multicast.c:1295:7-13: WARNING: PTR_ERR_OR_ZERO can be
used.

Reported-by: Abaci <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Zhong <abaci-bugfix@linux.alibaba.com>
Acked-by: Nikolay Aleksandrov <nikolay@nvidia.com>
Link: https://lore.kernel.org/r/1611542381-91178-1-git-send-email-abaci-bugfix@linux.alibaba.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>