ext4: no need to verify new add extent block

ext4_ext_grow_indepth will add a new extent block which has init the
expected content. We can mark this buffer as verified so to stop a
useless check in __read_extent_tree_block.

Signed-off-by: yangerkun <yangerkun@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20210609075545.1442160-1-yangerkun@huawei.com


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