USB: yurex: fix race between probe() and read()

There's a window during which read() would return 0 instead
of a correct error for no data yet. Reorder initialization
to fix the race.

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