[mips64][liftoff] Fix converting u32 to intptr

emit_u32_to_intptr should zero-extend the low 32 bits of the src.

Bug: v8:10925
Change-Id: I48135da054d5f30d7aa4d67918c839debc7cdb2f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2418031Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Zhao Jiazhong <zhaojiazhong-hf@loongson.cn>
Cr-Commit-Position: refs/heads/master@{#70024}

src/wasm/baseline/mips64/liftoff-assembler-mips64.h

@@ -919,7 +919,7 @@ I64_SHIFTOP_I(shr, dsrl)
 #undef I64_SHIFTOP_I
 
 void LiftoffAssembler::emit_u32_to_intptr(Register dst, Register src) {
-  addu(dst, src, zero_reg);
+  Dext(dst, src, 0, 32);
 }
 
 void LiftoffAssembler::emit_f32_neg(DoubleRegister dst, DoubleRegister src) {