e1000e: Remove unreachable code

msi-x interrupts are not shared so there's no need to check if the
interrupt was really from this adapter.

Signed-off-by: Benjamin Poirier <bpoirier@suse.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>