btrfs-progs: test/fsck/020: Cleanup custom check function by overriding check_image function

Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

tests/fsck-tests/020-extent-ref-cases/test.sh

@@ -1,6 +1,6 @@
 #!/bin/bash
-# In order to confirm that btrfsck supports to check a variety of refs, add the
-# following cases:
+# In order to confirm that 'btrfs check' supports checking a variety of refs,
+# add the following cases:
 #
 # * keyed_block_ref
 # * keyed_data_ref
@@ -19,12 +19,11 @@ source "$TOP/tests/common"
 
 check_prereq btrfs
 
-for img in *.img *.raw.xz
-do
-	image=$(extract_image "$img")
+check_image() {
+	local image
 
-	# Since the return value bug is already fixed, we don't need
-	# the old grep hack to detect bug.
+	image=$1
 	run_check "$TOP/btrfs" check "$image"
-	rm -f "$image"
-done
+}
+
+check_all_images