linux-firmware: update definition for atheros ar9271

ar9271.fw is the old convention for the firmware.
Starting with kernel 3.0 the new convention is htc_9271.fw which is a
newer version of the firmware so symlinking won't do it and there are no
guarantees that the newer firmware will work with the older driver
either.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Acked-by: Alexandre Pereira da Silva <aletes.xgr@gmail.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>