ACPI / fan: Fix error reading cur_state

On some platforms with ACPI4 variable speed fan, reading cur_state from
cooling device returns "invalid value" error. This confuses user space
applications.

This issue occurs as the current driver doesn't take account of
"FineGrainControl" from _FIF(Fan Information). When the "FineGrainControl"
is set, _FSL(FSL Set Level) takes argument as a percent, which doesn't
have to match from any control value from _FPS(Fan Performance States).
It is also possible that the Fan is not actually running at the requested
speed returning a lower speed.
On some platforms the BIOS is setting fan speed to a level during boot,
which will not have an exact match to _FPS control values. The current
implementation will treat this level as invalid value.

The simple change is to atleast return state corresponding to a maximum
control value in the _FPS compared to the current level.

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>