UIO: uio_pdrv: fix license specification

Thanks to Magnus Damm for pointing that out.

Signed-off-by: Uwe Kleine-König <Uwe.Kleine-Koenig@digi.com>
Cc: Magnus Damm <magnus.damm@gmail.com>
Acked-by: Hans J. Koch <hjk@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>