HID: elecom: add support for EX-G M-XT4DRBK trackball

This patch enables the 6th button on the ELECOM EX-G M-XT4DRBK
trackball mouse.

This is a left handed EX-G variant which only comes in a wireless (D)
model. It has a total of 6 buttons but one of these is not available
because of how the HID descriptor is configured.

Signed-off-by: Tomasz Kramkowski <tk@the-tk.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
diff --git a/drivers/hid/hid-ids.h b/drivers/hid/hid-ids.h
index 830c022..c8902f2 100644
--- a/drivers/hid/hid-ids.h
+++ b/drivers/hid/hid-ids.h
@@ -373,6 +373,7 @@
 #define USB_DEVICE_ID_ELECOM_BM084	0x0061
 #define USB_DEVICE_ID_ELECOM_M_XT3URBK	0x00fb
 #define USB_DEVICE_ID_ELECOM_M_XT3DRBK	0x00fc
+#define USB_DEVICE_ID_ELECOM_M_XT4DRBK	0x00fd
 #define USB_DEVICE_ID_ELECOM_M_DT1URBK	0x00fe
 #define USB_DEVICE_ID_ELECOM_M_DT1DRBK	0x00ff
 #define USB_DEVICE_ID_ELECOM_M_HT1URBK	0x010c