Correct test and escape earlier

usr/share/rear/layout/prepare/default/250_compare_disks.sh

@@ -75,12 +75,12 @@ if ! is_true "$MIGRATION_MODE" ; then
     local current_disk_name=''
     local current_size=''
     for current_device_path in /sys/block/* ; do
+        # Continue with next block device if the device is a multipath device slave
+        is_multipath_path ${current_device_path#/sys/block/} || continue
         # Continue with next block device if the current one has no queue directory:
         test -d $current_device_path/queue || continue
         # Continue with next block device if no size can be read for the current one:
         test -r $current_device_path/size || continue
-        # Continue with next block device if the device is a multipath device slave
-        test is_multipath_path /dev/$current_device_path || continue
         current_disk_name="${current_device_path#/sys/block/}"
         current_size=$( get_disk_size $current_disk_name )
         test "$current_size" -gt '0' && replacement_hardware_disk_sizes=( "${replacement_hardware_disk_sizes[@]}" "$current_size" )