ieee802154: cc2520: Fix space before , coding style issue

This patch removes the warnings (space before , ) shown by
checkpatch.pl

Signed-off-by: Mohammad Jamal <md.jamalmohiuddin@gmail.com>
Acked-by: Varka Bhadram <varkabhadram@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>