tcg: Fix next_tb type in cpu_exec

Reviewed-by: Aurelien Jarno <aurelien@aurel32.net>
Signed-off-by: Richard Henderson <rth@twiddle.net>

cpu-exec.c

@@ -209,7 +209,7 @@ int cpu_exec(CPUArchState *env)
     int ret, interrupt_request;
     TranslationBlock *tb;
     uint8_t *tc_ptr;
-    tcg_target_ulong next_tb;
+    uintptr_t next_tb;
 
     if (cpu->halted) {
         if (!cpu_has_work(cpu)) {