image-buildr: Fixup bootargs for luks boot

This works around librem5-devkit-base putting an
unencrypted root device into flash-kernel's boot
args.

Librem5/librem5-devkit-tools#32

root.sh

@@ -94,6 +94,11 @@ EOF
   # Hack up cryttab until askpass supports it
   sed -i 's%discard%discard,keyscript=/usr/bin/osk-sdl-keyscript%' "${basedir}/etc/crypttab"
   chroot "${basedir}" update-initramfs -u
+
+  # Work around https://source.puri.sm/Librem5/librem5-devkit-tools/-/issues/32
+  BLKID=$(sudo blkid -c /dev/null -o value -s 'UUID' /dev/mapper/crypt_root)
+  sed -i "s%root=[^\"]\\+%root=UUID=${BLKID}%" "${basedir}/etc/flash-kernel/ubootenv.d/root"
+  chroot "${basedir}" flash-kernel
 }
 
 function cleanup_cryptroot()