sunrpc: kernel BUG at kernel/cred.c:825!

Init missing debug member magic with CRED_MAGIC.
Signed-off-by: Santosh kumar pradhan <santoshkumar.pradhan@wdc.com>
Reported-by: Dave Jones <davej@codemonkey.org.uk>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

net/sunrpc/auth.c

@@ -41,6 +41,9 @@ static unsigned long number_cred_unused;
 
 static struct cred machine_cred = {
 	.usage = ATOMIC_INIT(1),
+#ifdef CONFIG_DEBUG_CREDENTIALS
+	.magic = CRED_MAGIC,
+#endif
 };
 
 /*