tune2fs: fix dereference of freed memory after journal replay

This can be found by running the test t_replay_and_set under valgrind.

Reported-by: Chris Clayton <chris2553@googlemail.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
diff --git a/misc/tune2fs.c b/misc/tune2fs.c
index 723f7ae..b8cddfa 100644
--- a/misc/tune2fs.c
+++ b/misc/tune2fs.c
@@ -3051,6 +3051,7 @@
 				ext2fs_close_free(&fs);
 			exit(1);
 		}
+		sb = fs->super;
 	}
 #endif