e1000e: cleanup hw.h

Remove unnecessary #include, forward prototype of struct e1000_adapter and
an empty comment; fix a comment which mentions "static data for the MAC"
which is not applicable to the following struct; and cleanup some
whitespace issues.

Signed-off-by: Bruce Allan <bruce.w.allan@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>