RDMA/nes: Use WARN()

Use WARN() rather than printk() followed by WARN_ON(1), for conciseness.

A simplified version of the semantic patch that makes this transformation
is as follows: (http://coccinelle.lip6.fr/

)

// <smpl>
@@
expression list es;
@@

-printk(
+WARN(1,
  es);
-WARN_ON(1);
// </smpl>

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>

[ Remove extra KERN_ERR from WARN() format.  - Roland ]

Signed-off-by: Roland Dreier <roland@purestorage.com>