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: Iabd182eeb4fbdc67f4e07b40a1b593471cf8cbdf
Signed-off-by: Anil kumar mamidala <amami@codeaurora.org>