msm: pm2: fix the bug in standalone idle statistics

msm_pm_standalone_power_collapse function is always returning
success irrespective of actual gdfs status. There could be possiblilty
that wfi can fail which needs to be consider while measuring the
standalone power collapse statistics.

Change-Id: I643bc4344cf1299cd8de5e6d7d88579e5e9a704d
Signed-off-by: Anji jonnala <anjir@codeaurora.org>