ACPICA: Parser: Fix a regression in LoadTable support

ACPICA commit a78506e0ce8ab1d20db2a055d99cf9143e89eb29

LoadTable allows an alternative RootPathString than the default "\", while
the new table execution support fails to keep this logic.

This regression can be detected by ASLTS - TLT0.tst4, this patch fixes this
regression.

Linux upstream is not affected by this regression as we haven't enabled the
new table execution support there. BZ 1326, Lv Zheng.

Link: https://github.com/acpica/acpica/commit/a78506e0
Link: https://bugs.acpica.org/show_bug.cgi?id=1326


Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>