ia64: fix format string for ia64-acpi-cpu-freq

ia64: fix format string for ia64-acpi-cpu-freq

Fix warning with %lx / s64 mismatch:

  CC [M]  drivers/cpufreq/ia64-acpi-cpufreq.o
    drivers/cpufreq/ia64-acpi-cpufreq.c: In function 'processor_get_pstate':
      warning: format '%lx' expects argument of type 'long unsigned int',
      but argument 3 has type 's64' {aka 'long long int'} [-Wformat=]

Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>