SUNRPC refactor rpcauth_checkverf error returns

Most of the time an error from the credops crvalidate function means the
server has sent us a garbage verifier. The gss_validate function is the
exception where there is an -EACCES case if the user GSS_context on the client
has expired.

Signed-off-by: Andy Adamson <andros@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/net/sunrpc/auth_null.c b/net/sunrpc/auth_null.c
index 4664eb4..f0ebe07 100644
--- a/net/sunrpc/auth_null.c
+++ b/net/sunrpc/auth_null.c
@@ -88,13 +88,13 @@
 	flavor = ntohl(*p++);
 	if (flavor != RPC_AUTH_NULL) {
 		printk("RPC: bad verf flavor: %u\n", flavor);
-		return NULL;
+		return ERR_PTR(-EIO);
 	}
 
 	size = ntohl(*p++);
 	if (size != 0) {
 		printk("RPC: bad verf size: %u\n", size);
-		return NULL;
+		return ERR_PTR(-EIO);
 	}
 
 	return p;