Changed variable references

Changed variable references, as it helps minimize diff when forking off a compatability package with fixed .so version, such as libprotobuf23 which can then use the $pkgbase variable to access the src/ but $pkgname can be different to target pacman conflicts nicely

This is not super important, and I wouldn't be in the know of what sort of issues this might cause as I haven't dealt with split packages before (all I really know about pkgbase).

But if it just resolves to the same string, it felt harmless to change.