cpmac: use print_mac() instead of MAC_FMT

Switch to using DECLARE_MAC_BUF/print_mac() added by commit
0795af57

 [NET]: Introduce and use print_mac()
and DECLARE_MAC_BUF().

Signed-off-by: Eugene Konev <ejka@imfi.kspu.ru>
Signed-off-by: Jeff Garzik <jeff@garzik.org>