Prevent crash on modulo by zero

19370955 "Prevent crash on division by zero" fixed a crash when attempting
a division by zero using the / operator in a dts.  However, it missed the
precisely equivalent crash with the % (modulus) operator.  This patch fixes
the oversight.

Reported-by: Anton Blanchard <anton@samba.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>