pch_gbe: improve coding style

This patch clears up a few coding style issues:

- Makes two function definitions a bit nicer looking.
- Remove unneeded parentheses.
- Simplify macros for register bits.

[ RC - Rebased Takahiro's changes and wrote a commit message
  explaining the changes. ]

Signed-off-by: Takahiro Shimizu <tshimizu818@gmail.com>
Signed-off-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>