cpuidle: coupled: remove unused define cpuidle_coupled_lock

cpuidle: coupled: remove unused define cpuidle_coupled_lock

commit 75274b33e779ae40a750bcb4bd0b07c4dfef4746 upstream.

This was found with the -RT patch enabled, but the fix should apply to
non-RT also.

Used multi_v7_defconfig+PREEMPT_RT_FULL=y and this caused a compilation
warning without this fix:
../drivers/cpuidle/coupled.c:122:21: warning: 'cpuidle_coupled_lock'
defined but not used [-Wunused-variable]

Signed-off-by: Anders Roxell <anders.roxell@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Mike Galbraith <mgalbraith@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>