[AMDGPU] Fix promote alloca with double use in a same insn

If we have an instruction where more than one pointer operands
are derived from the same promoted alloca, we are fixing it for
one argument and do not fix a second use considering this user
done.

Fix this by deferring processing of memory intrinsics until all
potential operands are replaced.

Fixes: SWDEV-271358

Differential Revision: https://reviews.llvm.org/D96386