ACPICA: Fix possible memory leak.

Ensure cleanup after a memory allocation failure in dsmethod.c.
Original Linux change from Jesper Juhl.

Signed-off-by: Jesper Juhl <jj@chaosbits.net>
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>