USB: make ksuspend_usbd thread non-freezable

This patch (as1012b) makes the ksuspend_usbd kernel thread
non-freezable.  Since the PM core has been changed to lock all devices
during a system sleep, the thread no longer needs to be frozen.  It
won't interfere with a system sleep because before trying to resume a
root hub device, it acquires the device's lock.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>