USB: serial: option.c: Add chipset information for 4G W14

Carsten Juttner thankfully investigated a bit and found out some details
about the chipset used in the 4G W14 device I recently added to
option.c.

I think this information is useful for reference, so I'd be happy if you
could include those bits.
Signed-off-by: Gernot Hillier <gernot@hillier.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/serial/option.c

@@ -338,6 +338,8 @@ static int  option_resume(struct usb_serial *serial);
 
 /* 4G Systems products */
 #define FOUR_G_SYSTEMS_VENDOR_ID		0x1c9e
+/* This is the 4G XS Stick W14 a.k.a. Mobilcom Debitel Surf-Stick *
+ * It seems to contain a Qualcomm QSC6240/6290 chipset            */
 #define FOUR_G_SYSTEMS_PRODUCT_W14		0x9603
 
 /* Haier products */