igb: update the approach taken to acquiring and releasing the phy lock

The current approach is just using a ?: type mechanism to set the phy
locking bit.  This if fine for now but limits us to only 2.  Switch to a
nested if statement for future compatiblity with more than 2 phys.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>