Use the correct path for the loop device.

debian/changelog

@@ -1,3 +1,9 @@
+livecd-rootfs (2.831) UNRELEASED; urgency=medium
+
+  * Use the correct path for the loop device.
+
+ -- Steve Langasek <steve.langasek@ubuntu.com>  Mon, 17 Apr 2023 16:11:40 -0700
+
 livecd-rootfs (2.830) lunar; urgency=medium
 
   * Call losetup -d properly.

live-build/functions

@@ -70,7 +70,7 @@ mount_image() {
     fi
 
     # Find the rootfs location
-    rootfs_dev_mapper="/dev/mapper/${loop_device}p${rootpart}"
+    rootfs_dev_mapper="${loop_device}p${rootpart}"
     if [ ! -b "${rootfs_dev_mapper}" ]; then
         echo "${rootfs_dev_mapper} is not a block device";
         exit 1