RDMA/nes: Fix incorrect unlock in nes_process_mac_intr()

Commit ce6e74f2 ("RDMA/nes: Make nesadapter->phy_lock usage
consistent") introduced a problem where phy_lock was only unlocked
within an if statement and so nes_process_mac_intr() could return with
phy_lock still held.  Fix this.

This was discovered because of the sparse warning:

    drivers/infiniband/hw/nes/nes_hw.c:2643:9: warning: context imbalance in 'nes_process_mac_intr' - different lock contexts for basic block

Reported-by: Roland Dreier <rdreier@cisco.com>
Signed-off-by: Chien Tung <chien.tin.tung@intel.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>