If the status value returned by acpi_install_address_space_handler()
in ec_install_handlers() is AE_NOT_FOUND, it is treated in a special
way, apparently because it might mean a _REG method evaluation
failure (at least that is the case according to the comment in
there), but acpi_install_address_space_handler() does not take
_REG evaluation errors into account at all, so the AE_NOT_FOUND
special handling is confusing at best.

For this reason, change ec_install_handlers() to stop the EC and
return -ENODEV on all acpi_install_address_space_handler() errors.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>