ASoC: fsl: check property 'compatible' for the machine name

Check /compatible rather than /model to determine the machine name.
The p1022ds older device trees get a different /model from the new
ones, while /compatible is consistent there, so checking /compatible
will save the bother of detecting older p1022ds device trees.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Acked-by: Timur Tabi <timur@freescale.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>