net: dsa: vitesse-vsc73xx: Convert to plain comments to avoid kerneldoc warnings

The comments before struct vsc73xx_platform and struct vsc73xx_spi use
kerneldoc format, but then fail to document the members of these
structures. All the structure members are self evident, and the driver
has not other kerneldoc comments, so change these to plain comments to
avoid warnings.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>