RDMA/uverbs: Annotate uverbs_request_next_ptr() return value as a __user pointer

This patch avoids that sparse complains about a mismatch between the
returned value and the function return type.

Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
Fixes: c3bea3d2dc ("RDMA/uverbs: Use the iterator for ib_uverbs_unmarshall_recv()")
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/core/uverbs_cmd.c

@@ -162,7 +162,7 @@ static const void __user *uverbs_request_next_ptr(struct uverbs_req_iter *iter,
 	const void __user *res = iter->cur;
 
 	if (iter->cur + len > iter->end)
-		return ERR_PTR(-ENOSPC);
+		return (void __force __user *)ERR_PTR(-ENOSPC);
 	iter->cur += len;
 	return res;
 }