IB/umem: Fix use of npages/nmap fields

In ib_umem structure npages holds original number of sg entries, while
nmap is number of DMA blocks returned by dma_map_sg.

Fixes: c5d76f13 ('IB/core: Add umem function to read data from user-space')
Signed-off-by: Artemy Kovalyov <artemyko@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/core/umem.c

@@ -352,7 +352,7 @@ int ib_umem_copy_from(void *dst, struct ib_umem *umem, size_t offset,
 		return -EINVAL;
 	}
 
-	ret = sg_pcopy_to_buffer(umem->sg_head.sgl, umem->nmap, dst, length,
+	ret = sg_pcopy_to_buffer(umem->sg_head.sgl, umem->npages, dst, length,
 				 offset + ib_umem_offset(umem));
 
 	if (ret < 0)