net/mlx4_core: Fix checking order in MR table init

In procedure mlx4_init_mr_table(), slaves should do no processing,
but should return success. This initialization is hypervisor-only.

However, the check for num_mpts being a power-of-2 was performed
before the check to return immediately if the driver is for a slave.
This resulted in spurious failures.

The order of performing the checks is reversed, so that if the
driver is for a slave, no processing is done and success is returned.

Signed-off-by: Jack Morgenstein <jackm@dev.mellanox.co.il>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>