msm: lpm_levels: return new idle level to cpuidle framework

Need to return the new idle level to cpuidle framework
but just returned input value argument 'index' which is
not used actually at lpm_cpu_power_select().

CRs-fixed: 601636
Change-Id: Id82ad9e558b1797fe50175dcb7cd7200146fcb92
Signed-off-by: Anil kumar mamidala <amami@codeaurora.org>