ext4: factor out ext4_fill_raw_inode()

Factor out ext4_fill_raw_inode() from ext4_do_update_inode(), which is
use to fill the in-mem inode contents into the inode table buffer, in
preparation for initializing the exclusive inode buffer without reading
the block in __ext4_get_inode_loc().

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20210901020955.1657340-2-yi.zhang@huawei.com


Signed-off-by: Theodore Ts'o <tytso@mit.edu>