ext4: ext4_get_{dev}_journal return proper error value

ext4_get_journal() and ext4_get_dev_journal() return NULL if they failed
to init journal, making them return proper error value instead, also
rename them to ext4_open_{inode,dev}_journal().

[ Folded fix to ext4_calculate_overhead() to check for an ERR_PTR
  instead of NULL. ]

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20230811063610.2980059-13-yi.zhang@huaweicloud.com


Reported-by:  <syzbot+b3123e6d9842e526de39@syzkaller.appspotmail.com>
Link: https://lore.kernel.org/r/20230826011029.2023140-1-yi.zhang@huaweicloud.com


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