e1000e: Fix duplicate include guard

The include guard "_E1000_HW_H_" is used by header files in three
different drivers (e1000/e1000_hw.h, e1000e/hw.h, and igb/e1000_hw.h).
Using the same include guard macro in more than one header file may
cause unexpected behavior from the compiler. Fix the duplicate include
guard in the e1000e driver by renaming it.

Fixes: bc7f75fa

 ("[E1000E]: New pci-express e1000 driver (currently for ICH9 devices only)")
Signed-off-by: Tom Seewald <tseewald@gmail.com>
Tested-by: Dvora Fuxbrumer <dvorax.fuxbrumer@linux.intel.com>
Acked-by: Sasha Neftin <sasha.neftin@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>