ext2: fix some incorrect comments in inode.c

There are some incorrect comments in inode.c, so fix them
properly.

Link: https://lore.kernel.org/r/20200703124411.24085-1-cgxu519@mykernel.net


Signed-off-by: Chengguang Xu <cgxu519@mykernel.net>
Signed-off-by: Jan Kara <jack@suse.cz>