ARM: OMAP2+: Fix warning for omap_init_time_of()

Fix warning: no previous prototype for 'omap_init_time_of'.

Fixes: e69b4e1a ("ARM: OMAP2+: Add omap_init_time_of()")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>