input: mouse_set should check input device type.

Otherwise, the index of an input device like a usb-kbd is silently accepted.

(qemu) info mice
  Mouse #2: QEMU PS/2 Mouse
* Mouse #3: QEMU HID Mouse
(qemu) mouse_set 1
(qemu) info mice
  Mouse #2: QEMU PS/2 Mouse
* Mouse #3: QEMU HID Mouse

Also replace monitor_printf() call in do_mouse_set() with error_report() and
adjust error message.

Signed-off-by: Hani Benhabiles <hani@linux.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
