target-m68k: fix a typo in 'P' packet processing

Attached is a patch to fix a typo in 'P' packet processing for M68K.

Without this patch, QEMU fails to honor GDB's P packets from GDB
(writing to registers) for the address registers (A0 - A7).

The problem is because of an obvious typo.  Notice that the second
"if" condition is meant to be n < 16 in:

  if (n < 8) {
    :
  } else if (n < 8) {

Signed-off-by: Kazu Hirata <kazu@codesourcery.com>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>

gdbstub.c

@@ -1014,7 +1014,7 @@ static int cpu_gdb_write_register(CPUState *env, uint8_t *mem_buf, int n)
     if (n < 8) {
         /* D0-D7 */
         env->dregs[n] = tmp;
-    } else if (n < 8) {
+    } else if (n < 16) {
         /* A0-A7 */
         env->aregs[n - 8] = tmp;
     } else {