with thin provisioning, use the overlay size, not the base image size

Using the overlay size in the device mapper table allows the filesystem in the base image to be extended if the overlay is larger than the base image (e.g. `resize2fs /dev/mapper/live-rw`).

modules.d/90dmsquash-live/dmsquash-live-root.sh

@@ -298,7 +298,7 @@ do_live_overlay() {
         dmsetup message /dev/mapper/live-overlay-pool 0 "create_thin 0"
 
         # Create a snapshot of the base image
-        echo 0 "$sz" thin /dev/mapper/live-overlay-pool 0 "$base" | dmsetup create live-rw
+        echo 0 "$thin_data_sz" thin /dev/mapper/live-overlay-pool 0 "$base" | dmsetup create live-rw
     elif [ -z "$overlayfs" ]; then
         echo 0 "$sz" snapshot "$base" "$over" PO 8 | dmsetup create live-rw
     fi