Fix address space for function pointers with qualifier

This patch fixes a bug introduced in commit 4eaf5846. Commit
4eaf5846 sets address space of function type as program
address space unconditionally. This breaks types which have
address space qualifiers. E.g. __ptr32.

This patch fixes the bug by using address space qualifiers if
present.

Differential Revision: https://reviews.llvm.org/D119045