ath5k: enable EEPROM checksum check

Without this we have no gaurantee of the integrity of the
EEPROM and are likely to encounter a lot of bogus bug reports
due to actual issues on the EEPROM. With the EEPROM checksum
check in place we can easily rule those issues out.

If you run patch during a revert *you* have a card with a busted
EEPROM and only older kernel will support that concoction. This
patch is a trade off between not accepitng bogus EEPROMs and
avoiding bogus bug reports allowing developers to focus instead
on real concrete issues.

If stable keeps bogus bug reports because of a possibly busted EEPROM
feel free to apply this there too.

Tested on an AR5414

Cc: stable@kernel.org
Cc: jirislaby@gmail.com
Cc: akpm@linux-foundation.org
Cc: rjw@sisk.pl
Cc: me@bobcopeland.com
Cc: david.quan@atheros.com
Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>