net: macb: Fix coding style warnings

This commit takes care of the coding style warnings
that are mostly due to a different comment style and
lines over 80 chars, as well as a dangling else.

Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Moritz Fischer <moritz.fischer@ettus.com>
Signed-off-by: David S. Miller <davem@davemloft.net>