net: dsa: fix copyright holder

I do not hold the copyright of the DSA core and drivers source files,
since these changes have been written as an initiative of my day job.
Fix this.

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