asus-laptop: fix incorrect return value for write_acpi_int_ret if handle is NULL

According to the comments of write_acpi_int_ret(), write_acpi_int_ret()
should return 0 if write is successful, -1 else.  Thus if handle is NULL,
the write does not happen, it should return -1.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Cc: Matthew Garrett <mjg@redhat.com>
Cc: Corentin Chary <corentincj@iksaif.net>
Cc: Alan Jenkins <alan-jenkins@tuffmail.co.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Matthew Garrett <mjg@redhat.com>