igb: Drop unnecessary write of E1000_IMS from igb_msix_other

Since we mask interrupts in EIMS not in IMS there is no need to re-enable
mask bits in that register.  As such we can remove the write to IMS from
the end of igb_msix_other.

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>