x86/intel_rdt/cqm: Make integer rmid_limbo_count static

rmid_limbo_count is local to the source and does not need to be in global
scope, so make it static.

Cleans up sparse warning:
symbol 'rmid_limbo_count' was not declared. Should it be static?

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: kernel-janitors@vger.kernel.org
Link: https://lkml.kernel.org/r/20171002145931.27479-1-colin.king@canonical.com