ACPICA: Fix possible memory leak in dispatcher error path.

On error, delete mutex object created during method mutex creation.
Reported by tim.gardner@canonical.com.

Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>