ipq40xx: R619AC: replace space with - separator in variant string

ipq40xx: R619AC: replace space with - separator in variant string

Kalle:
"I see that variant has a space in it, does that work it correctly? My
original idea was that spaces would not be allowed, but didn't realise
to add a check for that."

Is this an easy change? Because the original author (Tim Davis) noted:
"You may substitute the & and space with something else saner if they
prove to be problematic."

Signed-off-by: Christian Lamparter <chunkeey@gmail.com>