cpuidle/coupled: Remove redundant 'dev' argument of cpuidle_state_is_coupled()

For cpuidle_state_is_coupled(), 'dev' is not used, so remove it.

Signed-off-by: Xunlei Pang <pang.xunlei@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>