Make the serial driver framework work with CONFIG_SERIAL_MULTI enabled
diff --git a/drivers/ns9750_serial.c b/drivers/ns9750_serial.c
index 8dff367..02c0d39 100644
--- a/drivers/ns9750_serial.c
+++ b/drivers/ns9750_serial.c
@@ -35,6 +35,10 @@
 
 DECLARE_GLOBAL_DATA_PTR;
 
+#if !defined(CONFIG_CONS_INDEX)
+#error "No console index specified."
+#endif
+
 #define CONSOLE CONFIG_CONS_INDEX
 
 static unsigned int calcBitrateRegister( void );