jbd2: sparse pointer use of zero as null

Get rid of sparse related warnings from places that use integer as NULL
pointer.  (Ported from upstream ext3/jbd changes.)
Signed-off-by: Mingming Cao <cmm@us.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

fs/jbd2/transaction.c

@@ -1182,7 +1182,7 @@ int jbd2_journal_dirty_metadata(handle_t *handle, struct buffer_head *bh)
 	}
 
 	/* That test should have eliminated the following case: */
-	J_ASSERT_JH(jh, jh->b_frozen_data == 0);
+	J_ASSERT_JH(jh, jh->b_frozen_data == NULL);
 
 	JBUFFER_TRACE(jh, "file as BJ_Metadata");
 	spin_lock(&journal->j_list_lock);
@@ -1532,7 +1532,7 @@ void __jbd2_journal_temp_unlink_buffer(struct journal_head *jh)
 
 	J_ASSERT_JH(jh, jh->b_jlist < BJ_Types);
 	if (jh->b_jlist != BJ_None)
-		J_ASSERT_JH(jh, transaction != 0);
+		J_ASSERT_JH(jh, transaction != NULL);
 
 	switch (jh->b_jlist) {
 	case BJ_None:
@@ -1601,11 +1601,11 @@ __journal_try_to_free_buffer(journal_t *journal, struct buffer_head *bh)
 	if (buffer_locked(bh) || buffer_dirty(bh))
 		goto out;
 
-	if (jh->b_next_transaction != 0)
+	if (jh->b_next_transaction != NULL)
 		goto out;
 
 	spin_lock(&journal->j_list_lock);
-	if (jh->b_transaction != 0 && jh->b_cp_transaction == 0) {
+	if (jh->b_transaction != NULL && jh->b_cp_transaction == NULL) {
 		if (jh->b_jlist == BJ_SyncData || jh->b_jlist == BJ_Locked) {
 			/* A written-back ordered data buffer */
 			JBUFFER_TRACE(jh, "release data");
@@ -1613,7 +1613,7 @@ __journal_try_to_free_buffer(journal_t *journal, struct buffer_head *bh)
 			jbd2_journal_remove_journal_head(bh);
 			__brelse(bh);
 		}
-	} else if (jh->b_cp_transaction != 0 && jh->b_transaction == 0) {
+	} else if (jh->b_cp_transaction != NULL && jh->b_transaction == NULL) {
 		/* written-back checkpointed metadata buffer */
 		if (jh->b_jlist == BJ_None) {
 			JBUFFER_TRACE(jh, "remove from checkpoint list");
@@ -1973,7 +1973,7 @@ void __jbd2_journal_file_buffer(struct journal_head *jh,
 
 	J_ASSERT_JH(jh, jh->b_jlist < BJ_Types);
 	J_ASSERT_JH(jh, jh->b_transaction == transaction ||
-				jh->b_transaction == 0);
+				jh->b_transaction == NULL);
 
 	if (jh->b_transaction && jh->b_jlist == jlist)
 		return;