ASoC: Intel: mrfld: return error codes when an error occurs

Currently function sst_platform_get_resources always returns zero and
error return codes set by the function are never returned. Fix this
by returning the error return code in variable ret rather than the
hard coded zero.

Addresses-Coverity: ("Unused value")
Fixes: f533a035

 ("ASoC: Intel: mrfld - create separate module for pci part")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Cezary Rojewski <cezary.rojewski@intel.com>
Acked-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20200208220720.36657-1-colin.king@canonical.com
Signed-off-by: Mark Brown <broonie@kernel.org>