asus-wmi: use ASUS_WMI_METHODID_DSTS2 as default DSTS ID.

According to responses from the BIOS team, ASUS_WMI_METHODID_DSTS2
(0x53545344) will be used as future DSTS ID. In addition, calling
asus_wmi_evaluate_method(ASUS_WMI_METHODID_DSTS2, 0, 0, NULL) returns
ASUS_WMI_UNSUPPORTED_METHOD in new ASUS laptop PCs. This patch fixes
no DSTS ID will be assigned in this case.

Signed-off-by: Alex Hung <alex.hung@canonical.com>
Signed-off-by: Matthew Garrett <mjg@redhat.com>
Cc: stable@kernel.org