USB: serial: ch341: add new Product ID

commit 5563b3b6 upstream.

Add PID for CH340 that's found on cheap programmers.

The driver works flawlessly as soon as the new PID (0x9986) is added to it.
These look like ANU232MI but ship with a ch341 inside. They have no special
identifiers (mine only has the string "DB9D20130716" printed on the PCB and
nothing identifiable on the packaging. The merchant i bought it from
doesn't sell these anymore).

the lsusb -v output is:
Bus 001 Device 009: ID 9986:7523
Device Descriptor:
  bLength                18
  bDescriptorType         1
  bcdUSB               1.10
  bDeviceClass          255 Vendor Specific Class
  bDeviceSubClass         0
  bDeviceProtocol         0
  bMaxPacketSize0         8
  idVendor           0x9986
  idProduct          0x7523
  bcdDevice            2.54
  iManufacturer           0
  iProduct                0
  iSerial                 0
  bNumConfigurations      1
  Configuration Descriptor:
    bLength            ...

drivers/usb/serial/ch341.c

@@ -85,6 +85,7 @@ static const struct usb_device_id id_table[] = {
 	{ USB_DEVICE(0x1a86, 0x7522) },
 	{ USB_DEVICE(0x1a86, 0x7523) },
 	{ USB_DEVICE(0x4348, 0x5523) },
+	{ USB_DEVICE(0x9986, 0x7523) },
 	{ },
 };
 MODULE_DEVICE_TABLE(usb, id_table);