uwb: fix use of del_timer_sync() in interrupt

del_timer_sync() cannot be used in interrupt.
Replace it with del_timer() and a flag

Signed-off-by: Oliver Neukum <oneukum@suse.de>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>