asus-laptop: correct error handling in sysfs_acpi_set

Properly return rv back to the caller in the case of an error in
parse_arg. In the process remove a unused variable 'out'.

Signed-off-by: Giedrius Statkevičius <giedrius.statkevicius@gmail.com>
Signed-off-by: Darren Hart <dvhart@linux.intel.com>