ext4: Fix mmap/truncate race when blocksize < pagesize && !nodellaoc

This patch fixes the mmap/truncate race that was fixed for delayed
allocation by merging ext4_{journalled,normal,da}_writepage() into
ext4_writepage().

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Acked-by: Jan Kara <jack@suse.cz>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>