ARM: dts: imx51-zii-rdu1: set name prefix for TPA6130A2

Set a sound name prefix for the HPA, as otherwise the sound controls
naming will clash with the controls of the DAC.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>