cpufreq: intel_pstate: Fix static checker warning for epp variable

Fix warning for:
drivers/cpufreq/intel_pstate.c:731 store_energy_performance_preference()
error: uninitialized symbol 'epp'.

This warning is for a case, when energy_performance_preference attribute
matches pre defined strings. In this case the value of raw epp will not
be used to set EPP bits in MSR_HWP_REQUEST. So initializing with any
value is fine.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>