Check if sensor is accessible on flush

In cases where halVersion is less than or equal to 1 or the sensor is
virtual the sensor service does not first check that the sensor is
accessible. This was causing failures for tests where a virtual sensor
was used because the flush command was not returning error. Now
INVALID_OPERATION is returned when flush is called on an idle sensor.

Test: set IGNORE_HARDWARE_FUSION to true and cts-tradefed && run cts -m
CtsSensorTestCases -t
android.hardware.cts.SensorTest#testBatchAndFlushUidIdle which fails
before this change, but passes now
Bug: 160282248

Change-Id: I6860bcdb9be341b5e2025caf7606d071779c9b39