xprtrdma: Do not leak an MW during a DMA map failure

Based on code audit.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Tested-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
diff --git a/net/sunrpc/xprtrdma/fmr_ops.c b/net/sunrpc/xprtrdma/fmr_ops.c
index 4837ced..6c4527b 100644
--- a/net/sunrpc/xprtrdma/fmr_ops.c
+++ b/net/sunrpc/xprtrdma/fmr_ops.c
@@ -257,6 +257,7 @@
 out_dmamap_err:
 	pr_err("rpcrdma: failed to dma map sg %p sg_nents %u\n",
 	       mw->mw_sg, mw->mw_nents);
+	rpcrdma_defer_mr_recovery(mw);
 	return -ENOMEM;
 
 out_maperr: