dt-bindings: net: dsa: ksz9477: fix indentation for switch spi bindings

Switch bindings for spi managed mode are using spaces instead of tabs.
Fix them to get a file with a proper kernel indentation style.
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>