igb: eliminate hw from the hw_dbg macro arguments

Various cosmetic cleanups. Comment fixes. Eliminate the hw part out
of the hw_dbg macro since it's always used.

Signed-off-by: Auke Kok <auke-jan.h.kok@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>