target/rx: Set exception vector base to 0xffffff80

The documentation says the vector is at 0xffffff80, instead of the
previous value of 0xffffffc0. That value must have been a bug because
the standard vector values (20, 21, 23, 25, 30) were all
past the end of the array.

Signed-off-by: Keith Packard <keithp@keithp.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

target/rx/helper.c

@@ -88,7 +88,7 @@ void rx_cpu_do_interrupt(CPUState *cs)
         cpu_stl_data(env, env->isp, env->pc);
 
         if (vec < 0x100) {
-            env->pc = cpu_ldl_data(env, 0xffffffc0 + vec * 4);
+            env->pc = cpu_ldl_data(env, 0xffffff80 + vec * 4);
         } else {
             env->pc = cpu_ldl_data(env, env->intb + (vec & 0xff) * 4);
         }