net: bridge: mcast: Use ERR_CAST instead of ERR_PTR(PTR_ERR())

Use ERR_CAST inlined function instead of ERR_PTR(PTR_ERR(...)).

net/bridge/br_multicast.c:1246:9-16: WARNING: ERR_CAST can be used with mp
Generated by: scripts/coccinelle/api/err_cast.cocci

Signed-off-by: Xu Wang <vulab@iscas.ac.cn>
Link: https://lore.kernel.org/r/20210204070549.83636-1-vulab@iscas.ac.cn


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