* Adjust the comment to reflect the fact that SIGBUS can occur not only
if the file is truncated, but also if an I/O error occurs while paging
in any part of it.
* Instead of setting a flag, just return EIO.
* Adjust the unit test accordingly.
MFC after: 1 week
Sponsored by: Klara, Inc.
Reviewed by: thj, kevans
Differential Revision: https://reviews.freebsd.org/D55108
(cherry picked from commit a689bfa4e25af8307709dc12f75b0e02a65abf18)