vxge: fix return of a free'd memblock on a failed dma mapping

Currently if a pci dma mapping failure is detected a free'd
memblock address is returned rather than a NULL (that indicates
an error). Fix this by ensuring NULL is returned on this error case.

Addresses-Coverity: ("Use after free")
Fixes: 528f7272 ("vxge: code cleanup and reorganization")
Signed-off-by: NColin Ian King <colin.king@canonical.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/neterion/vxge/vxge-config.c

@@ -2366,6 +2366,7 @@ static void *__vxge_hw_blockpool_malloc(struct __vxge_hw_device *devh, u32 size,
 				dma_object->addr))) {
 			vxge_os_dma_free(devh->pdev, memblock,
 				&dma_object->acc_handle);
+			memblock = NULL;
 			goto exit;
 		}