xprtrdma: fix incorrect header size calculations

commit 9122884 upstream.

Currently the header size calculations are using an assignment
operator instead of a += operator when accumulating the header
size leading to incorrect sizes.  Fix this by using the correct
operator.

Addresses-Coverity: ("Unused value")
Fixes: 302d3de ("xprtrdma: Prevent inline overflow")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
[bwh: Backported to 4.14: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

net/sunrpc/xprtrdma/rpc_rdma.c

@@ -75,7 +75,7 @@ static unsigned int rpcrdma_max_call_header_size(unsigned int maxsegs)
 
 	/* Maximum Read list size */
 	maxsegs += 2;	/* segment for head and tail buffers */
-	size = maxsegs * sizeof(struct rpcrdma_read_chunk);
+	size += maxsegs * sizeof(struct rpcrdma_read_chunk);
 
 	/* Minimal Read chunk size */
 	size += sizeof(__be32);	/* segment count */
@@ -101,7 +101,7 @@ static unsigned int rpcrdma_max_reply_header_size(unsigned int maxsegs)
 
 	/* Maximum Write list size */
 	maxsegs += 2;	/* segment for head and tail buffers */
-	size = sizeof(__be32);		/* segment count */
+	size += sizeof(__be32);		/* segment count */
 	size += maxsegs * sizeof(struct rpcrdma_segment);
 	size += sizeof(__be32);	/* list discriminator */