[OpenCL] Fix missing addrspace on implicit move assignment operator

This fixes the missing address space on `this` in the implicit move
assignment operator.
The function called here is an abstraction around the lines that have
been removed which also sets the address space correctly.
This is copied from CopyConstructor, CopyAssignment and MoveConstructor,
all of which use this function, and now MoveAssignment does too.

Fixes: PR50259

Reviewed By: svenvh

Differential Revision: https://reviews.llvm.org/D103252