Linux 6.9: Fix UBSAN errors in zap_micro.c

You can use the UBSAN_SANITIZE_* Kbuild options to exclude certain
kernel objects from the UBSAN checks. We previously excluded
zap_micro.o with:

UBSAN_SANITIZE_zap_micro.o := n

For some reason that didn't work for the 6.9 kernel, which wants us
to use:

UBSAN_SANITIZE_zfs/zap_micro.o := n

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tony Hutter <hutter2@llnl.gov>
Closes #16278
Closes #16330