tcg: Fix highwater check

A simple typo in the variable to use when comparing vs the highwater mark.
Reports are that qemu can in fact segfault occasionally due to this mistake.
Signed-off-by: NJohn Clarke <johnc@kirriwa.net>
Signed-off-by: NRichard Henderson <rth@twiddle.net>

tcg/tcg.c

@@ -2443,7 +2443,7 @@ int tcg_gen_code(TCGContext *s, tcg_insn_unit *gen_code_buf)
            one operation beginning below the high water mark cannot overrun
            the buffer completely.  Thus we can test for overflow after
            generating code without having to check during generation.  */
-        if (unlikely(s->code_gen_ptr > s->code_gen_highwater)) {
+        if (unlikely((void *)s->code_ptr > s->code_gen_highwater)) {
             return -1;
         }
     }