ath: add missing regdomain pair 0x5c mapping

Joe Culler reported a problem with his AR9170 device:

> ath: EEPROM regdomain: 0x5c
> ath: EEPROM indicates we should expect a direct regpair map
> ath: invalid regulatory domain/country code 0x5c
> ath: Invalid EEPROM contents

It turned out that the regdomain 'APL7_FCCA' was not mapped yet.
According to Luis R. Rodriguez [Atheros' engineer] APL7 maps to
FCC_CTL and FCCA maps to FCC_CTL as well, so the attached patch
should be correct.

Cc: <stable@kernel.org>
Reported-by: Joe Culler <joe.culler@gmail.com>
Acked-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: Christian Lamparter <chunkeey@googlemail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>