Linux 6.9: Fix UBSAN errors in sa.c

[tonyhutter]

Motivation and Context

Workaround UBSAN errors in sa.c on 6.9 kernels.
Closes #16278
Closes #16330

Description

This is a follow-on to 156a641 that ignores UBSAN errors in sa.c.
Thank you @thwalker3 for the fix.

How Has This Been Tested?

You can trigger the UBSAN error with this on Fedora 40 with 6.9.9 kernel:

truncate -s 100M file
sudo ./zpool create tank `pwd`/file
sudo cp -a /var/log /tank
< out of disk space >
dmesg

Using this PR, the errors do not appear.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Breaking change (fix or feature that would cause existing functionality to change)
• Library ABI change (libzfs, libzfs_core, libnvpair, libuutil and libzfsbootenv)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the OpenZFS code style requirements.
• I have updated the documentation accordingly.
• I have read the contributing document.
• I have added tests to cover my changes.
• I have run the ZFS Test Suite with this change applied.
• All commit messages are properly formatted and contain Signed-off-by.

[mcmilk]

Yes, this is the better way to do it.