RDMA/mad: Convert BUG_ONs to error flows

[ Upstream commit 2468b82d69e3a53d024f28d79ba0fdb8bf43dfbf ]

Let's perform checks in-place instead of BUG_ONs.

Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>