ext4: update ext4_data_block_valid related comments

Since ext4_data_block_valid() has been renamed to ext4_inode_block_valid(),
the related comments need to be updated.

Signed-off-by: Chunguang Xu <brookxu@tencent.com>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Link: https://lore.kernel.org/r/1604764698-4269-5-git-send-email-brookxu@tencent.com


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