x86/pmstat: restore changes lost by "consolidation"

Both c6e0a5539623 ("cpufreq: use existing local var in
cpufreq_statistic_init()") and a1ce987411f6 ("cpufreq: don't leave stale
statistics pointer") were lost in the course of "moving" the code,
presumably due to overly lax re-basing.

Fixes: bf0cd071db2a ("xen/pmstat: consolidate code into pmstat.c")
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>