ext4: fix error code saved on super block during file system abort

ext4_abort will eventually call ext4_errno_to_code, which translates the
errno to an EXT4_ERR specific error.  This means that ext4_abort expects
an errno.  By using EXT4_ERR_ here, it gets misinterpreted (as an errno),
and ends up saving EXT4_ERR_EBUSY on the superblock during an abort,
which makes no sense.

ESHUTDOWN will get properly translated to EXT4_ERR_SHUTDOWN, so use that
instead.

Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
Link: https://lore.kernel.org/r/20211026173302.84000-1-krisman@collabora.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>