cpufreq: intel_pstate: Avoid redundant initialization of local vars

After commit 1a4fe38a ("cpufreq: intel_pstate: Remove max/min
fractions to limit performance") the initial value of the pstate local
variable in intel_pstate_max_within_limits() and the initial value of
the max_pstate local variable in intel_pstate_prepare_request() are
both immediately discarded, so initialize both these variables to
their target values upfront.

No intentional changes of behavior.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>