can: usb: Kconfig: Add PCAN-USB X6 device in help text

This patch adds a text line in the help section of the CAN_PEAK_USB
config item describing the support of the PCAN-USB X6 adapter, which is
already included in the Kernel since 4.9.

Signed-off-by: Stephane Grosjean <s.grosjean@peak-system.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/usb/Kconfig

@@ -73,6 +73,7 @@ config CAN_PEAK_USB
 	  PCAN-USB FD          single CAN-FD channel USB adapter
 	  PCAN-USB Pro FD      dual CAN-FD channels USB adapter
 	  PCAN-Chip USB        CAN-FD to USB stamp module
+	  PCAN-USB X6          6 CAN-FD channels USB adapter
 
 	  (see also http://www.peak-system.com).