ACPI: Fix conflict between customized DSDT and DSDT local copy

This patch fixes the following issue:
If DSDT is customized, no local DSDT copy is needed.

References: https://bugzilla.kernel.org/show_bug.cgi?id=69711


Signed-off-by: Enrico Etxe Arte <goitizena.generoa@gmail.com>
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Cc: 2.6.35+ <stable@vger.kernel.org> # 2.6.35+
[rjw: Subject]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>