ASoC: sigmadsp: Fix endianness conversion

Make sure to always convert the firmware data to local endianness before
using it.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Fixes: a35daac77a03 ("ASoC: sigmadsp: Add support for fw v2")
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@kernel.org>