mlx4_bf_alloc had an unnecessary/duplicate code line. Did no harm,
but not good practice.

Reported by the Mellanox Beijing team.
Signed-off-by: NJack Morgenstein <jackm@dev.mellanox.co.il>
Signed-off-by: NAmir Vadai <amirv@mellanox.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>