There is a lock unbalanced exit path in acpi_ds_initialize_method(),
this patch corrects it.

Fixes: 441ad11d (ACPICA: Dispatcher: Fix a mutex issue for method auto serialization)
Tested-by: NImre Deak <imre.deak@intel.com>
Signed-off-by: NLv Zheng <lv.zheng@intel.com>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>