tools/power/cpupower: fix compilation with STATIC=true

commit 9de9aa45 upstream.

Rename duplicate sysfs_read_file into cpupower_read_sysfs and fix linking.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Acked-by: Thomas Renninger <trenn@suse.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: Shuah Khan (Samsung OSG) <shuah@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>