tegra: Update Avionic Design vendor prefix

The official vendor prefix for Avionic Design is now "ad". Update the
board DTS files accordingly.

Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>
Acked-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Tom Warren <twarren@nvidia.com>

board/avionic-design/dts/tegra20-medcom.dts

@@ -4,7 +4,7 @@
 
 / {
 	model = "Avionic Design Medcom-Wide";
-	compatible = "avionic-design,medcom", "nvidia,tegra20";
+	compatible = "ad,medcom", "nvidia,tegra20";
 
 	aliases {
 		usb0 = "/usb@c5008000";

board/avionic-design/dts/tegra20-plutux.dts

@@ -4,7 +4,7 @@
 
 / {
 	model = "Avionic Design Plutux";
-	compatible = "avionic-design,plutux", "nvidia,tegra20";
+	compatible = "ad,plutux", "nvidia,tegra20";
 
 	aliases {
 		usb0 = "/usb@c5008000";

board/avionic-design/dts/tegra20-tec.dts

@@ -4,7 +4,7 @@
 
 / {
 	model = "Avionic Design Tamonten Evaluation Carrier";
-	compatible = "avionic-design,tec", "nvidia,tegra20";
+	compatible = "ad,tec", "nvidia,tegra20";
 
 	aliases {
 		usb0 = "/usb@c5008000";