ASoC: omap: Fix incorrect ARM dependency

Commit b0e0a4d6

 ("ASoC: omap: Enable COMPILE_TEST build for DT platforms")
added two incorrect CONFIG_ARCH_ARM dependencies making impossible to select
audio support for Nokia RX-51. Fix this by using correct CONFIG_ARM.

Signed-off-by: Jarkko Nikula <jarkko.nikula@bitmer.com>
Signed-off-by: Mark Brown <broonie@linaro.org>