Linux 6.9: Fix UBSAN errors in sa.c (#16380)

This is a follow-on to 156a64161b4f9da35f2e0484106173344cf78317
that ignores UBSAN errors in sa.c.

Thank you @thwalker3 for the fix.

Original-patch-by: @thwalker3
Signed-off-by: Tony Hutter <hutter2@llnl.gov>
Closes #16278
Closes #16330
Reviewed-by: Tino Reichardt <milky-zfs@mcmilk.de>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>