ARM: OMAP2+: Fix mismerge for omap_hwmod_get_main_clk() API

Commit ac5b0ea3 (Merge tag 'omap-devel-f-for-3.6'...) had a merge
conflict that somehow got incorrecly resolved in a lossy way for
commit bed9d1bb

 (ARM: OMAP2+: hwmod: add omap_hwmod_get_main_clk() API).
Fix the issue by applying the missing pieces.

Reported-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>