ASoC: SOF: loader: fix snd_sof_fw_parse_ext_data

ASoC: SOF: loader: fix snd_sof_fw_parse_ext_data

An error occurs during parsing more than one ext_data from the mailbox, because
of invalid data offset handling. Fix by removing the incorrect duplicate
increment of the offset.

The return value is also reset in the switch case. This does not change the
behavior but improves readability - there is no longer a need to check what the
return value of get_ext_windows is.

Signed-off-by: Karol Trzcinski <karolx.trzcinski@linux.intel.com>
Signed-off-by: Bartosz Kokoszko <bartoszx.kokoszko@linux.intel.com>
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20191210004854.16845-4-pierre-louis.bossart@linux.intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>