[GVN] Bug fix to reportMayClobberedLoad remark

Bug fix to avoid assert crashing when generating remarks for GVN crashing.

Intention of assert is correct but ignores edge case of instructions being equivalent.

Reduced input that causes crash when remarks are turned on:
```
target datalayout = "e-m:o-i64:64-i128:128-n32:64-S128"
target triple = "arm64-apple-macosx12.0.0"

define ptr @ReplaceWithTidy(ptr %zz_hold) {
cond.end480.us:
  %0 = load ptr, ptr null, align 8
  store ptr %0, ptr %0, align 8
  store ptr null, ptr %zz_hold, align 8
  %1 = load ptr, ptr %0, align 8
  store ptr %1, ptr null, align 8
  ret ptr null
}
```

Reviewed By: fhahn

Differential Revision: https://reviews.llvm.org/D129235