tune2fs: fix uninitialized variable in remove_journal_device

This bug was introduced by commit 7dfefaf413bbd ("tune2fs: update
journal super block when changing UUID for fs").

Fixes-Coverity-Bug: 1229243

Reported-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
diff --git a/misc/tune2fs.c b/misc/tune2fs.c
index 0c1feb1..639809d 100644
--- a/misc/tune2fs.c
+++ b/misc/tune2fs.c
@@ -232,7 +232,6 @@
 	errcode_t	retval;
 	int		commit_remove_journal = 0;
 	io_manager	io_ptr;
-	int start;
 
 	if (f_flag)
 		commit_remove_journal = 1; /* force removal even if error */
@@ -286,8 +285,9 @@
 	jsb->s_nr_users = htonl(nr_users);
 
 	/* Write back the journal superblock */
-	if ((retval = io_channel_write_blk64(jfs->io, start,
-	    -SUPERBLOCK_SIZE, buf))) {
+	if ((retval = io_channel_write_blk64(jfs->io,
+				ext2fs_journal_sb_start(fs->blocksize),
+				-SUPERBLOCK_SIZE, buf))) {
 		com_err(program_name, retval,
 			"while writing journal superblock.");
 		goto no_valid_journal;