synaptics-rmi: Fix Coverity issue that is impossible to hit in reality
synaptics-rmi: Fix Coverity issue that is impossible to hit in reality

The guint16 was promoted to (signed) int for the multiplication, which meant
that the highest address possible was 0x7FFFFFFF not 0xFFFFFFFF. Which doesn't
really matter in reality, as all addresses are much smaller than that now.

fwupd/fwupd,hughsie/fwupd,hughsie/fwupd,fwupd/fwupd,hughsie/fwupd,fwupd/fwupd,hughsie/fwupd,fwupd/fwupd