ARM: dts: imx6: ventana: change sound device name

The 'model' property in the imx-audio-sgtl5000 binding specifies the
user-visible name of the audio device. This should be something common and
not baseboard specific.

Signed-off-by: Tim Harvey <tharvey@gateworks.com>
Signed-off-by: Shawn Guo <shawn.guo@freescale.com>