e1000: consistently use the hw variables

It's rather confusing when adapter->hw and hw are mixed and matched
within a particular function.
Some of this was missed in cd1cf2fc1d49c509ded05dcd41b7600a5957fb9a
and r353778 respectively.

(cherry picked from commit c1655b0f8998f9e842a004f33e7c9c01c5d9e879)