powertop: fix error message

Application tries to use timer_stats module instead of cpufreq_stats.
Error message is printed if opening of the file /proc/timer_stats fails.

Signed-off-by: Lauri Hintsala <lauri.hintsala@bluegiga.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Merge git://busybox.net/busybox