Revert "[liftoff][arm64] Use 64 bit offset reg in mem op"

This reverts commit f645d0b8.

Reason for revert:
https://ci.chromium.org/p/v8/builders/ci/V8%20Mac%20-%20arm64%20-%20release/3544

Original change's description:
> [liftoff][arm64] Use 64 bit offset reg in mem op
>
> Accessing the Wasm memory with a 64 bit offset was truncated to 32 bit,
> which is fine if we check bounds first, but not if we rely on the
> trap handler to catch the OOB.
>
> R=​clemensb@chromium.org
>
> Bug: v8:11587
> Change-Id: I82a3a2906e55d9d640c30e770a5c93532e3a442c
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2808942
> Reviewed-by: Clemens Backes <clemensb@chromium.org>
> Commit-Queue: Thibaud Michaud <thibaudm@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#73829}

Bug: v8:11587
Change-Id: If7396981d43833f32ebc525c20abdbe78020e717
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2810785
Auto-Submit: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#73835}

src/wasm/baseline/arm64/liftoff-assembler-arm64.h

@@ -128,7 +128,7 @@ inline MemOperand GetMemOp(LiftoffAssembler* assm,
                            UseScratchRegisterScope* temps, Register addr,
                            Register offset, T offset_imm) {
   if (offset.is_valid()) {
-    if (offset_imm == 0) return MemOperand(addr.X(), offset.X());
+    if (offset_imm == 0) return MemOperand(addr.X(), offset.W(), UXTW);
     Register tmp = temps->AcquireX();
     DCHECK_GE(kMaxUInt32, offset_imm);
     assm->Add(tmp, offset.X(), offset_imm);