This matches licensing used by most of BCM5301X files and is preferred as:
1) GPL 2.0+ makes it clearly compatible with Linux kernel
2) MIT is also permissive but preferred over ISC

This file was fully developed by me.
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>