ref(base): Change initramfs created filename

Since void defaults to building an 'initramfs-<kernelversion>.img' file
when running the update hook, I think it is just correct if we follow
their example.

This will make it harder to distinguish between kernels if you have many
others in the boot dir (e.g. Arch, or LTS) but that seems only an edge
case.

roles/base/vars/main.yaml

@@ -1,5 +1,5 @@
 ---
-booster_initramfs_name: /boot/booster-void
+booster_initramfs_name: /boot/initramfs
 host_name: voider
 timezone: Europe/Berlin
 locales_enabled: