b43legacy: Fix possible NULL pointer dereference in DMA code

This fixes a possible NULL pointer dereference in an error path of the
DMA allocation error checking code. This is also necessary for a future
DMA API change that is on its way into the mainline kernel that adds
an additional dev parameter to dma_mapping_error().
Signed-off-by: Michael Buesch <mb@bu3sch.de>
Cc: stable <stable@kernel.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/b43legacy/dma.c

@@ -876,6 +876,7 @@ struct b43legacy_dmaring *b43legacy_setup_dmaring(struct b43legacy_wldev *dev,
 	if (!ring)
 		goto out;
 	ring->type = type;
+	ring->dev = dev;
 
 	nr_slots = B43legacy_RXRING_SLOTS;
 	if (for_tx)
@@ -922,7 +923,6 @@ struct b43legacy_dmaring *b43legacy_setup_dmaring(struct b43legacy_wldev *dev,
 				 DMA_TO_DEVICE);
 	}
 
-	ring->dev = dev;
 	ring->nr_slots = nr_slots;
 	ring->mmio_base = b43legacy_dmacontroller_base(type, controller_index);
 	ring->index = controller_index;