HID: make device_attribute const

Make this const as it is only passed as an argument to the function
device_create_file and device_remove_file and the corresponding arguments are
of type const.  Done using Coccinelle

Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>