power.stats: Modify wlan data provider to not fail if wifi off

Previous the WlanStateResidencyDataProvider was returning a failure when
it failed to open the wlan node to read the wlan power stats. This node
is not avaiable when wifi is off. Since this is intended behavior we
should not return a failure.

Bug: 130202935
Test: vts-tradefed run vts -m VtsHalPowerStatsV1_0Target
Change-Id: I9fa288bcb41c8ce07f40d580c1f82a809b3367f8
1 file changed