[Libomptarget] Fix warnings on address space attributes

The device runtime uses the address space attribute to control the
placement of important constants on the GPU. The changes made in D126061
caused these to start emitting errors as they were not applied to the
type. This patch fixes the issues to make the warnings go away.

Reviewed By: ye-luo

Differential Revision: https://reviews.llvm.org/D129896