jbd2: fix compile warning when using JBUFFER_TRACE

The jh pointer may be used uninitialized in the two cases below and the
compiler complain about it when enabling JBUFFER_TRACE macro, fix them.

In file included from fs/jbd2/transaction.c:19:0:
fs/jbd2/transaction.c: In function ‘jbd2_journal_get_undo_access’:
./include/linux/jbd2.h:1637:38: warning: ‘jh’ is used uninitialized in this function [-Wuninitialized]
#define JBUFFER_TRACE(jh, info) do { printk("%s: %d\n", __func__, jh->b_jcount);} while (0)
^
fs/jbd2/transaction.c:1219:23: note: ‘jh’ was declared here
struct journal_head *jh;
^
In file included from fs/jbd2/transaction.c:19:0:
fs/jbd2/transaction.c: In function ‘jbd2_journal_dirty_metadata’:
./include/linux/jbd2.h:1637:38: warning: ‘jh’ may be used uninitialized in this function [-Wmaybe-uninitialized]
#define JBUFFER_TRACE(jh, info) do { printk("%s: %d\n", __func__, jh->b_jcount);} while (0)
^
fs/jbd2/transaction.c:1332:23: note: ‘jh’ was declared here
struct journal_head *jh;
^

Signed-off-by: zhangyi (F) <[e-mail]>
Signed-off-by: Theodore Ts'o <[e-mail]>
Cc: [e-mail]
Reviewed-by: Jan Kara <[e-mail]>

fs/jbd2/transaction.c

···
 	struct journal_head *jh;
 	char *committed_data = NULL;
 
-	JBUFFER_TRACE(jh, "entry");
 	if (jbd2_write_access_granted(handle, bh, true))
 		return 0;
 
 	jh = jbd2_journal_add_journal_head(bh);
+	JBUFFER_TRACE(jh, "entry");
+
 	/*
 	 * Do this first --- it can drop the journal lock, so we want to
 	 * make sure that obtaining the committed_data is done
···
 
 	if (is_handle_aborted(handle))
 		return -EROFS;
-	if (!buffer_jbd(bh)) {
-		ret = -EUCLEAN;
-		goto out;
-	}
+	if (!buffer_jbd(bh))
+		return -EUCLEAN;
+
 	/*
 	 * We don't grab jh reference here since the buffer must be part
 	 * of the running transaction.
 	 */
 	jh = bh2jh(bh);
+	jbd_debug(5, "journal_head %p\n", jh);
+	JBUFFER_TRACE(jh, "entry");
+
 	/*
 	 * This and the following assertions are unreliable since we may see jh
 	 * in inconsistent state unless we grab bh_state lock. But this is
···
 	}
 
 	journal = transaction->t_journal;
-	jbd_debug(5, "journal_head %p\n", jh);
-	JBUFFER_TRACE(jh, "entry");
-
 	jbd_lock_bh_state(bh);
 
 	if (jh->b_modified == 0) {