ARM: OMAP3+: DPLL: stop reparenting to same parent if already done

omap3_noncore_dpll_set_rate forces a reparent to the same clk_ref
for every call that takes place. This is an can be done only if a change
is detected.

Signed-off-by: Nishanth Menon <nm@ti.com>
Acked-by: Tero Kristo <t-kristo@ti.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>