smalloc: update use of ExternalArrayType constants

The constants in enum v8::ExternalArrayType have been changed. The old
values are there for legacy reasons, but it's best to update anyway.

Signed-off-by: Trevor Norris <trev.norris@gmail.com>
src: fix jslint warning

Signed-off-by: Trevor Norris <trev.norris@gmail.com>