platform/x86: eeepc-laptop: Skip unknown key messages 0x50 0x51

Otherwise those are printed several times when (un)plugging the AC
connector.

Signed-off-by: Pau Espin Pedrol <pespin.shar@gmail.com>
Acked-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org>