ASoC: SigmaDSP: Provide diagnostic error messages

Provide some error messages when loading the firmware fails, so it is possible
to diagnose the reason for the failure.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Acked-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>