net: phylink: move MLO_AN_FIXED resolve handling to if() statement

The switch() statement doesn't sit very well with the preceeding if()
statements, and results in excessive indentation that spoils code
readability. Begin cleaning this up by converting the MLO_AN_FIXED case
to an if() statement.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://patch.msgid.link/E1t9RQk-002Fen-1A@rmk-PC.armlinux.org.uk


Signed-off-by: Jakub Kicinski <kuba@kernel.org>