ath5k: avoid PCI FATAL interrupts by restoring RETRY_TIMEOUT disabling

This reverts 'ath5k: remove dummy PCI "retry timeout" fix' on the
same theory as in 'ath9k: Fix PCI FATAL interrupts by restoring
RETRY_TIMEOUT disabling'.

Reported-by: Bob Copeland <me@bobcopeland.com>
Cc: stable@kernel.org
Signed-off-by: John W. Linville <linville@tuxdriver.com>