Revert "ext4: fix superblock checksum calculation race"

This reverts commit acaa5326 which can
result in a ext4_superblock_csum_set() trying to sleep while a
spinlock is being held.

For more discussion of this issue, please see:

https://lore.kernel.org/r/000000000000f50cb705b313ed70@google.com



Reported-by:  <syzbot+7a4ba6a239b91a126c28@syzkaller.appspotmail.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>