tools/power/x86/intel-speed-select: Fix cpu-count output

I have a system with 28 threads/socket but intel-speed-select reports
a cpu-count of 29.

Fix an off-by-one error in the cpu_count() function.

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>