cpupower: Fix turbo frequency reporting for pre-Sandy Bridge cores

The switch that conditionally sets CPUPOWER_CAP_HAS_TURBO_RATIO and
CPUPOWER_CAP_IS_SNB flags is missing a break, so all cores get both
flags set and an assumed base clock of 100 MHz for turbo values.

Reported-by: GSR <gsr.bugs@infernal-iceberg.com>
Tested-by: GSR <gsr.bugs@infernal-iceberg.com>
References: https://bugs.debian.org/859978


Fixes: 8fb2e440 (cpupower: Show Intel turbo ratio support via ...)
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>