runtime: fix data sizes for res_search results

The return values are 32 bit, not 64 bit.

I don't think this would be the cause of any problems, but
it can't hurt to fix it.

Change-Id: Icdd50606360ab9d74070271f9d1721d5fe640bc7
Reviewed-on: https://go-review.googlesource.com/c/go/+/174518
Run-TryBot: Keith Randall <khr@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/runtime/lookup_darwin_amd64.s

@@ -34,7 +34,7 @@ TEXT runtime·res_search_trampoline(SB),NOSPLIT,$0
     MOVLQSX  (AX), DX             // move return from libc_error into DX
     XORL     AX, AX               // size on error is 0
 ok:
-    MOVQ    AX, 28(BX) // size
-    MOVQ    DX, 32(BX) // error code
+    MOVL    AX, 28(BX) // size
+    MOVL    DX, 32(BX) // error code
     POPQ    BP
     RET