ARM: dts: at91: VInCo: fix phy reset gpio flag

Fix gpio active flag for the phy reset-gpios property. The line is
active low instead of active high.
Actually, this flags was never used by the macb driver.

Reported-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Cc: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>