Fixes a possible memory leak in the error exit path introduced by
recent commit 388a9902 ("ACPICA: _OSI Support: handle any errors from
acpi_os_acquire_mutex()").

[rjw: Changelog]
Signed-off-by: NJung-uk Kim <jkim@FreeBSD.org>
Signed-off-by: NBob Moore <robert.moore@intel.com>
Signed-off-by: NLv Zheng <lv.zheng@intel.com>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>