Fix the following coccicheck warning:

net/bridge/br_private.h:1334:8-9: WARNING: return of 0/1 in function
'br_mrp_enabled' with return type bool

Fixes: 65369933 ("bridge: mrp: Integrate MRP into the bridge")
Signed-off-by: Jason Yan <yanaijie@huawei.com>
Acked-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>