igb: cleanup whitespace issues in igb_main.c

This patch goes through and cleans up whitespace issues in igb_main.c
to help improve readability.

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>