USB: ehci-au1xxx: fix suspend callback

Remove a stray 'return 0' at the top of the suspend callback,
and move au1xxx_stop_ehc() out of the ehci spinlock since it takes
some time to complete.

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