lpstate_idx remains uninitialized in the case when elapsed_time
is greater than MAX_RAMP_DOWN_TIME.  At the end of rampdown the
global pstate should be equal to the local pstate.

Fixes: 20b15b76 (cpufreq: powernv: Use PMCR to verify global and localpstate)
Reported-by: NStephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: NAkshay Adiga <akshay.adiga@linux.vnet.ibm.com>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>