ath9k: Fix regression on receiving PS poll frames

In the the patch:

ath9k: use new FIF_PSPOLL configure filter

I forgot to add the new FIF_PSPOLL to the supported mask.
Without this we mask out the FIF_PSPOLL flag therefore
we'd ignore it from mac80211.

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