cpufreq: intel_pstate: Use mutex guard for driver locking

cpufreq: intel_pstate: Use mutex guard for driver locking

Use guard(mutex)(&intel_pstate_driver_lock), or the scoped variant of
it, wherever intel_pstate_driver_lock needs to be held.

This allows some local variables and goto statements to be dropped as
they are not necessary any more.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Link: https://patch.msgid.link/2807232.mvXUDI8C0e@rafael.j.wysocki