net/mlx4: fix spelling mistake: "availible" -> "available"

Trivial fix to spelling mistakes in the mlx4 driver

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Yuval Shaia <yuval.shaia@oracle.com>
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>