ext4: remove the redundant folio_wait_stable()

__filemap_get_folio() with FGP_WRITEBEGIN parameter has already wait
for stable folio, so remove the redundant folio_wait_stable() in
ext4_da_write_begin(), it was left over from the commit cc883236
("ext4: drop unnecessary journal handle in delalloc write") that
removed the retry getting page logic.

Fixes: cc883236

 ("ext4: drop unnecessary journal handle in delalloc write")
Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20240419023005.2719050-1-yi.zhang@huaweicloud.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>