postmarketos-mkinitfs: don't fail without deviceinfo [skip ci]
Created by: ollieparanoid
When building device packages, the postmarketos-mkinitfs package gets installed as dependency of postmarketos-base. It must not try to create an initramfs at this point, when there is not deviceinfo file.
We build the initramfs during the installation, so it's fine.
Added [skip ci] because linux kernels and KDE updates are currently getting built for the binary repository (so Travis couldn't finish anyway).