ath9k_hw_getisr() doesn't appear to set anything in the status mask for
PCI FATAL or PERR interrupts (AR_INTR_SYNC_HOST1_FATAL/PERR), which
the open-source HAL seems to do.  This means that the card isn't reset
after these interrupts.

This patch seems to fix a problem where the wireless drops out with an
"ath9k: received PCI FATAL interrupt" in dmesg after some time; the
hardware is an AR5416 in an ASUS WL-500W running 2.6.28.7 (OpenWRT) and
compat-wireless 2009-03-31.
Signed-off-by: Steven Luo <steven@steven676.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>