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

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: Arvind Yadav <arvind.yadav.cs@gmail.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>