efivar: Try harder to find label's efimedia

[imp]

Summary

If there's no efimedia attribute on the provider, and the provider's a
glabel, then find the 'parent' geom. In this case, the provider's name
is label-type/name, but the geom's label will that of the underlying
device (eg ada0p1). If it is, recurisvely call find_geom_efimedia with
the geom's name, which shuold have the efimedia attribute.

Sponsored by: Netflix

[asomers]

I see nothing wrong with this, though I'm not very familiar with this library, and I don't know how to test it. However, there are two typos in your commit message, and the first line should read "libefivar" instead of "efivars".

lib/libefivar/efivar-dp-xlate.c

532

[imp]

Update per review