elfdump: chase ABI tag note name change from r232832
r232832 changed the ABI tag note name from .note.ABI-tag to .note.tag.
Follow suit in elfdump.
Elfdump's note parsing is very basic and should be significantly
reworked, but for now just restore the broken functionality.
Submitted by: martin at lispworks.com
MFC after: 1 week