USB: ehci-au1xxx does not need EHCI IO watchdog

I've been running variations of this patch for well over a year now;
my usual zoo of test devices didn't trigger any ill effects even
under heavy load.  As a nice sideeffect idle-wakeups are reduced
from 20/s to about 2/s (EHCI hub with mouse and kbd).

Signed-off-by: Manuel Lauss <manuel.lauss@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>