[RISCV] Don't use pointer operand in MemoryLocation for RISC-V strided and...

[RISCV] Don't use pointer operand in MemoryLocation for RISC-V strided and indexed load/store intrinsics. (#79890)

It seems that even though we set the size to unknown, there is still an
assumption in alias analysis somewhere that we will only access bytes
*after* the pointer. Since a strided/indexed load/store can have
negative indices, this is not accurate.

This was found in our downstream when the scheduler reordered a strided
load with negative stride above a scalar store that aliased with it.