ARM: OMAP3+: dpll: optimize noncore dpll locking logic

If the dpll is already locked, code can be optimized
to return much earlier than doing redundent set of lock mode
and wait on idlest.

Cc: Tony Lindgren <tony@atomide.com>
Cc: Jon Hunter <jon-hunter@ti.com>
Cc: Paul Walmsley <paul@pwsan.com>
Cc: Mike Turquette <mturquette@ti.com>
Signed-off-by: Vikram Pandita <vikram.pandita@ti.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>