ext4: fix typo in setup_new_flex_group_blocks

grop -> group

Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Link: https://lore.kernel.org/r/20230826174712.4059355-6-shikemeng@huaweicloud.com


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