ARM: OMAP: make ti81xx_rtc_hwmod static

The ti81xx_rtc_hwmod is not exported, or declared outside the file
arch/arm/mach-omap2/omap_hwmod_81xx_data.c so make it static to
avoid the following warning:

arch/arm/mach-omap2/omap_hwmod_81xx_data.c:246:19: warning: symbol 'ti81xx_rtc_hwmod' was not declared. Should it be static?
Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Signed-off-by: Tony Lindgren <tony@atomide.com>

arch/arm/mach-omap2/omap_hwmod_81xx_data.c

@@ -243,7 +243,7 @@ static struct omap_hwmod_class ti81xx_rtc_hwmod_class = {
 	.sysc		= &ti81xx_rtc_sysc,
 };
 
-struct omap_hwmod ti81xx_rtc_hwmod = {
+static struct omap_hwmod ti81xx_rtc_hwmod = {
 	.name		= "rtc",
 	.class		= &ti81xx_rtc_hwmod_class,
 	.clkdm_name	= "alwon_l3s_clkdm",