ARM: dts: imx53-ard: add regulators for lan9220

Since commit c7e963f6

 (net/smsc911x: Add regulator support), the lan9220
device tree probe fails on imx53-ard board, because the commit makes
VDD33A and VDDVARIO supplies mandatory for the driver.

Add a fixed dummy 3V3 supplying lan9220 to fix the regression.

Cc: stable@vger.kernel.org
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>