[media] ngene: properly handle __user ptr

Sparse is complaining about ngene's bad usage of a __user ptr:

>> drivers/media/pci/ngene/ngene-dvb.c:62:48: sparse: incorrect type in argument 2 (different address spaces)
drivers/media/pci/ngene/ngene-dvb.c:62:48: expected unsigned char const [usertype] *buf
drivers/media/pci/ngene/ngene-dvb.c:62:48: got char const [noderef] <asn:1>*buf

As this is intercepting a .write() file ops, we can't just memcpy. We need to use
copy_from_user.

Reported-by: kbuild test robot <[e-mail]>
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

drivers/media/dvb-core/dvb_ringbuffer.c

···
 	return len;
 }
 
+ssize_t dvb_ringbuffer_write_user(struct dvb_ringbuffer *rbuf,
+				  const u8 __user *buf, size_t len)
+{
+	int status;
+	size_t todo = len;
+	size_t split;
+
+	split = (rbuf->pwrite + len > rbuf->size) ? rbuf->size - rbuf->pwrite : 0;
+
+	if (split > 0) {
+		status = copy_from_user(rbuf->data+rbuf->pwrite, buf, split);
+		if (status)
+			return len - todo;
+		buf += split;
+		todo -= split;
+		rbuf->pwrite = 0;
+	}
+	status = copy_from_user(rbuf->data+rbuf->pwrite, buf, todo);
+	if (status)
+		return len - todo;
+	rbuf->pwrite = (rbuf->pwrite + todo) % rbuf->size;
+
+	return len;
+}
+
 ssize_t dvb_ringbuffer_pkt_write(struct dvb_ringbuffer *rbuf, u8* buf, size_t len)
 {
 	int status;
···
 EXPORT_SYMBOL(dvb_ringbuffer_read_user);
 EXPORT_SYMBOL(dvb_ringbuffer_read);
 EXPORT_SYMBOL(dvb_ringbuffer_write);
+EXPORT_SYMBOL(dvb_ringbuffer_write_user);

drivers/media/dvb-core/dvb_ringbuffer.h

···
 */
 extern ssize_t dvb_ringbuffer_write(struct dvb_ringbuffer *rbuf, const u8 *buf,
 				    size_t len);
+extern ssize_t dvb_ringbuffer_write_user(struct dvb_ringbuffer *rbuf,
+				         const u8 __user *buf, size_t len);
 
 
 /**

drivers/media/pci/ngene/ngene-dvb.c

···
 				     (&dev->tsout_rbuf) >= count) < 0)
 		return 0;
 
-	dvb_ringbuffer_write(&dev->tsout_rbuf, buf, count);
+	dvb_ringbuffer_write_user(&dev->tsout_rbuf, buf, count);
 
 	return count;
 }