ath9k: remove dangling error check on keycache reset on hw init

The keycache reset will not fail as right above we ensure
to set the sc->keymax to be <= ah->caps.keycache_size. Just remove
this dangling check.

Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>