V4L/DVB: TM6000: Fix code which cause memory corruption

The driver was doing malloc when buf is null causing memory corruption.

The analog part is still pretty much broken but at least fixing this
will stop it from crashing the machine when streamon.
Signed-off-by: NBee Hock Goh <beehock@gmail.com>
Signed-off-by: NMauro Carvalho Chehab <mchehab@redhat.com>

drivers/staging/tm6000/tm6000-video.c

@@ -491,7 +491,7 @@ static inline int tm6000_isoc_copy(struct urb *urb)
 	unsigned long copied;
 
 	get_next_buf(dma_q, &buf);
-	if (!buf)
+	if (buf)
 		outp = videobuf_to_vmalloc(&buf->vb);
 
 	if (!outp)