fix NULL pointer with MUSB and DMA on ISO ep

For the case of an isochonous endpoint, musb_write_fifo may be
called with a NULL buffer from musb_host_tx if DMA is enabled.
Remove DMA check and always supply a valid buffer as long as
the URB contains a valid buffer.
Signed-off-by: Hunyue Yau <hyau@mvista.com>
Acked-by: David Brownell <dbrownell@users.sourceforge.net>

drivers/usb/musb/musb_host.c

@@ -1268,7 +1268,7 @@ void musb_host_tx(struct musb *musb, u8 epnum)
 			d->actual_length = qh->segsize;
 			if (++qh->iso_idx >= urb->number_of_packets) {
 				done = true;
-			} else if (!dma) {
+			} else {
 				d++;
 				buf = urb->transfer_buffer + d->offset;
 				wLength = d->length;