Fix multicast flow rule leak on adding unicast rule failure.

Fixes: 038d2ef8 ('IB/mlx5: Add flow steering support')
Signed-off-by: NMaor Gottlieb <maorg@mellanox.com>
Signed-off-by: NLeon Romanovsky <leon@kernel.org>
Signed-off-by: NDoug Ledford <dledford@redhat.com>