cpufreq: speedstep: remove unused speedstep_get_state

The only caller of speedstep_get_state() was removed in commit d4019f0a
("cpufreq: move freq change notifications to cpufreq core"). So building
speedstep-smi.o now triggers a GCC warning:
    drivers/cpufreq/speedstep-smi.c:148:12: warning: 'speedstep_get_state' defined but not used [-Wunused-function]

Remove this unused function.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>