ext4: move ext4_file_dio_write() into ext4_file_write()

This commit doesn't actually change anything; it just moves code
around in preparation for some code simplification work.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Reviewed-by: Jan Kara <jack@suse.cz>

diff --cc fs/ext4/file.c
Simple merge