tools/power/x86/intel-speed-select: Fix memory leak

cpumasks are allocated by calling the alloc_cpu_mask() function and are
never free'd.  They should be free'd after the commands have run.

Fix the memory leaks by calling free_cpu_set().

Signed-off-by: Prarit Bhargava <prarit@redhat.com>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Cc: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Cc: David Arcari <darcari@redhat.com>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>