Revert "tools: cpupower: fix return checks for sysfs_get_idlestate_count()"

This reverts commit 16b7c275c055cc36218404b5d147be7f76575087.

My previous commit 16b7c275c055 ("tools: cpupower: fix return checks for
sysfs_get_idlestate_count()") was not correct.  After looking
at the changelog for cpupower I noticed that Thomas had changed the return of
sysfs_get_idlestate_count() to an unsigned int to simplify the code.  The
problem is really that both he (in his original change) and I (in my new
change) missed the obvious that sysfs_get_idlestate_count()
can't return -ENODEV.  It should just return 0 for "no c-states".

Fixes: 16b7c275c055 (tools: cpupower: fix return checks for ...)
Signed-off-by: Prarit Bhargava <prarit@redhat.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>