cpmac: fix all checkpatch errors and warnings

This patches fixes a couple of checkpatch warnings and errors:
- lines over 80 columns
- printk() instead of pr_cont()
- assignments in tests (if ((foo == bar())))

Signed-off-by: Florian Fainelli <florian@openwrt.org>
Signed-off-by: David S. Miller <davem@davemloft.net>