ACPICA commit 9a6ecc9ec9ee067cad51eec539230bf494421d76

Since AE_ALREADY_EXISTS has already been converted to AE_OK in
acpi_ev_install_region_handlers(), this patch simplies a return value
check. Lv Zheng.

Link: https://github.com/acpica/acpica/commit/9a6ecc9eSigned-off-by: NLv Zheng <lv.zheng@intel.com>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>