jbd: Use offset_in_page() instead of manual calculation

Signed-off-by: Namhyung Kim <namhyung@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>

fs/jbd/transaction.c

@@ -711,7 +711,7 @@ done:
 		J_EXPECT_JH(jh, buffer_uptodate(jh2bh(jh)),
 			    "Possible IO failure.\n");
 		page = jh2bh(jh)->b_page;
-		offset = ((unsigned long) jh2bh(jh)->b_data) & ~PAGE_MASK;
+		offset = offset_in_page(jh2bh(jh)->b_data);
 		source = kmap_atomic(page, KM_USER0);
 		memcpy(jh->b_frozen_data, source+offset, jh2bh(jh)->b_size);
 		kunmap_atomic(source, KM_USER0);