Make sure RF5592 is set for RT5592 chip which apparently sometimes
doesn't have RF defined (but always comes with RF5592).
This patch was originally submitted on linux-wireless by
Tom Psyborg <pozega.tomislav@gmail.com> but got rejected.
Turns out the patch is actually needed.
Reported-by: Sebastian Gottschall <s.gottschall@dd-wrt.com>
Signed-off-by: Daniel Golle <daniel@makrotopia.org>
