devmatch: Ignore the pnp fields tagged as ignore ('#')

When matching entries, we should ignore those with a name of '#'. It's
the standard way to skip elements and need to be present to have the
proper offsets to the fields that are observed. No bus has a pnp
attribute of '#' and that is now disallowed for future buses that are
written.

Sponsored by: Netflix
Reviewed by: kbowling
Differential Revision: https://reviews.freebsd.org/D31482