serial.c: Fix build breakage introduced with commit e3c78c9b

This patch fixes the compilation problem introduced with commit
e3c78c9b [ppc4xx: Remove now unused CONFIG_UART1_CONSOLE]:

-> ./MAKEALL TB5200
Configuring for TB5200 board...
serial.c: In function '__default_serial_console':
serial.c:94: warning: no return statement in function returning non-void

I accidentally removed an "#else" line. This patch adds it back.

Signed-off-by: Stefan Roese <sr@denx.de>

common/serial.c

@@ -54,6 +54,7 @@ struct serial_device *__default_serial_console (void)
 #else
 #error "Bad CONFIG_CONS_INDEX."
 #endif
+#else
 	return &serial0_device;
 #endif
 #elif defined(CONFIG_MPC512X)