mkosi: Move generic disk partition before root partition

Otherwise we can't grow the root partition.

diff --git a/mkosi/mkosi.repart/20-disk.conf b/mkosi/mkosi.repart/10-disk.conf
similarity index 100%
rename from mkosi/mkosi.repart/20-disk.conf
rename to mkosi/mkosi.repart/10-disk.conf

diff --git a/mkosi/mkosi.repart/10-root.conf b/mkosi/mkosi.repart/20-root.conf
similarity index 100%
rename from mkosi/mkosi.repart/10-root.conf
rename to mkosi/mkosi.repart/20-root.conf