tcg: Reset data_gen_ptr correctly

This pointer needs to be reset after overflow just like
code_buf and code_ptr.

Cc: qemu-stable@nongnu.org
Fixes: 57a269469db ("tcg: Infrastructure for managing constant pools")
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Reviewed-by: LIU Zhiwei <zhiwei_liu@linux.alibaba.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

tcg/tcg.c

@@ -1399,7 +1399,6 @@ TranslationBlock *tcg_tb_alloc(TCGContext *s)
         goto retry;
     }
     qatomic_set(&s->code_gen_ptr, next);
-    s->data_gen_ptr = NULL;
     return tb;
 }
 
@@ -6172,6 +6171,7 @@ int tcg_gen_code(TCGContext *s, TranslationBlock *tb, uint64_t pc_start)
      */
     s->code_buf = tcg_splitwx_to_rw(tb->tc.ptr);
     s->code_ptr = s->code_buf;
+    s->data_gen_ptr = NULL;
 
 #ifdef TCG_TARGET_NEED_LDST_LABELS
     QSIMPLEQ_INIT(&s->ldst_labels);