rtlwifi: Use is_zero_ether_addr, remove line continuation

Use the normal kernel facilities and use %pM
to print the all zero mac address.

Remove unnecessary line continuation.

Signed-off-by: Joe Perches <joe@perches.com>
Acked-by:  <Larry.Finger@lwfinger.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>