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

These files were created and ever touched by a group of four people
only: Felix, INAGAKI, Hauke and me.
Signed-off-by: NRafał Miłecki <rafal@milecki.pl>
Acked-by: NFelix Fietkau <nbd@nbd.name>
Acked-by: NINAGAKI Hiroshi <musashino.open@gmail.com>
Acked-by: NHauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: NFlorian Fainelli <f.fainelli@gmail.com>