ath5k: do not release irq across suspend/resume

Paraphrasing Rafael J. Wysocki: "drivers should not release PCI IRQs
in suspend."  Doing so causes a warning during suspend/resume on some
platforms.

Cc: Rafael J. Wysocki <rjw@sisk.pl>
Reported-by: Alan Jenkins <alan-jenkins@tuffmail.co.uk>
Signed-off-by: Bob Copeland <me@bobcopeland.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>