IB/core: fix unmap_sg argument

__ib_umem_release calls dma_unmap_sg with a different number of
sg_entries than ib_umem_get uses for dma_map_sg. This might cause
trouble for implementations that merge sglist entries and results
in the following dma debug complaint:

DMA-API: device driver frees DMA sg list with different entry
         count [map count=2] [unmap count=1]

Fix it by using the correct value.
Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/core/umem.c

@@ -51,7 +51,7 @@ static void __ib_umem_release(struct ib_device *dev, struct ib_umem *umem, int d
 
 	if (umem->nmap > 0)
 		ib_dma_unmap_sg(dev, umem->sg_head.sgl,
-				umem->nmap,
+				umem->npages,
 				DMA_BIDIRECTIONAL);
 
 	for_each_sg(umem->sg_head.sgl, sg, umem->npages, i) {