[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
Fix this by deferring processing of memory intrinsics until all
potential operands are replaced.
Differential Revision: https://reviews.llvm.org/D96386