ext4: Fix BUG_ON at fs/buffer.c:652 in no journal mode

Calls to ext4_handle_dirty_metadata should only pass in an inode
pointer for inode-specific metadata, and not for shared metadata
blocks such as inode table blocks, block group descriptors, the
superblock, etc.

The BUG_ON can get tripped when updating a special device (such as a
block device) that is opened (so that i_mapping is set in
fs/block_dev.c) and the file system is mounted in no journal mode.

Addresses-Google-Bug: #2404870

Signed-off-by: Curt Wohlgemuth <curtw@google.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/fs/ext4/ext4_jbd2.c b/fs/ext4/ext4_jbd2.c
index 2f407c4..53d2764 100644
--- a/fs/ext4/ext4_jbd2.c
+++ b/fs/ext4/ext4_jbd2.c
@@ -125,7 +125,7 @@
 			ext4_journal_abort_handle(where, __func__, bh,
 						  handle, err);
 	} else {
-		if (inode && bh)
+		if (inode)
 			mark_buffer_dirty_inode(bh, inode);
 		else
 			mark_buffer_dirty(bh);