staging: pi433: fixed signedness of 4th argument to kfifo_from_user

sparse warning:
incorrect type in initializer (different signedness)
expected unsigned int *__copied, got int *<noident>
Signed-off-by: Stefano Manni <stefano.manni@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/pi433/pi433_if.c

@@ -716,7 +716,8 @@ pi433_write(struct file *filp, const char __user *buf,
 {
 	struct pi433_instance	*instance;
 	struct pi433_device	*device;
-	int                     copied, retval;
+	int                     retval;
+	unsigned int		copied;
 
 	instance = filp->private_data;
 	device = instance->device;