ARM: OMAP2+: Fix serial init for device tree based booting

We don't want to call omap_serial_early_init() for device
tree based booting as the ports are initialized based on
the .dts entries.
Reviewed-by: Kevin Hilman <khilman@linaro.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>

arch/arm/mach-omap2/serial.c

@@ -176,6 +176,9 @@ static char *cmdline_find_option(char *str)
 
 static int __init omap_serial_early_init(void)
 {
+	if (of_have_populated_dt())
+		return -ENODEV;
+
 	do {
 		char oh_name[MAX_UART_HWMOD_NAME_LEN];
 		struct omap_hwmod *oh;