igb: Make certain one vector is always assigned in igb_request_irq
This change makes certain that one interrupt is always initialized in
igb_request_irq. In addition we drop the use of adapter->pdev and
instead just call pdev since we made a local copy of the pointer earlier in
the function.
Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com> Tested-by: Aaron Brown <aaron.f.brown@intel.com> Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>