SUNRPC: Ensure get_rpccred() and put_rpccred() can take NULL arguments

Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
diff --git a/include/linux/sunrpc/auth.h b/include/linux/sunrpc/auth.h
index 6f36b2b..8997915 100644
--- a/include/linux/sunrpc/auth.h
+++ b/include/linux/sunrpc/auth.h
@@ -202,7 +202,8 @@
 static inline
 struct rpc_cred *	get_rpccred(struct rpc_cred *cred)
 {
-	atomic_inc(&cred->cr_count);
+	if (cred != NULL)
+		atomic_inc(&cred->cr_count);
 	return cred;
 }