net: phy: Correct Cygnus/Omega PHY driver prompt

The tristate prompt should have been replaced rather than defined a few
lines below, rebase mistake.

Fixes: 17cc9821

 ("net: phy: Move Omega PHY entry to Cygnus PHY driver")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>