Input: powermate - constify usb_device_id and fix space before '[' error

usb_device_id are not supposed to change at runtime. All functions
working with usb_device_id provided by <linux/usb.h> work with
const usb_device_id. So mark the non-const structs as const.

Fix checkpatch.pl error:
ERROR: space prohibited before open square bracket '['.
Signed-off-by: NArvind Yadav <arvind.yadav.cs@gmail.com>
Signed-off-by: NDmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/misc/powermate.c

@@ -432,7 +432,7 @@ static void powermate_disconnect(struct usb_interface *intf)
 	}
 }
 
-static struct usb_device_id powermate_devices [] = {
+static const struct usb_device_id powermate_devices[] = {
 	{ USB_DEVICE(POWERMATE_VENDOR, POWERMATE_PRODUCT_NEW) },
 	{ USB_DEVICE(POWERMATE_VENDOR, POWERMATE_PRODUCT_OLD) },
 	{ USB_DEVICE(CONTOUR_VENDOR, CONTOUR_JOG) },