ACPICA: Tables: Fix a regression in acpi_tb_find_table()

In the following commit, the return value of acpi_tb_find_table() is
incorrect:

commit ac0f06eb
Author: Lv Zheng <lv.zheng@intel.com>
Date:   Wed Sep 7 14:07:24 2016 +0800

    ACPICA: Tables: Tune table mutex to be a leaf lock

    ACPICA commit f564d57c6501b97a2871f0b4c048e79910f71783

This causes LoadTable opcode to fail. Fix this mistake.

Signed-off-by: Lv Zheng <lv.zheng@intel.com>
[ rjw: Changelog ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>