ASoC: SDCA: Add missing forward declaration in header

ASoC: SDCA: Add missing forward declaration in header

The structure sdca_function_desc contains a fwnode_handle which is
undefined if the user doesn't pull in an appropriate header. Add a
forward declaration to avoid this.

Fixes: 996bf834d0b6 ("ASoC: SDCA: Add code to parse Function information")
Tested-by: Bard Liao <yung-chuan.liao@linux.intel.com>
Reviewed-by: Maciej Strozek <mstrozek@opensource.cirrus.com>
Reviewed-by: Peter Ujfalusi <peter.ujfalusi@linux.intel.com>
Tested-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Link: https://patch.msgid.link/20251120153023.2105663-4-ckeepax@opensource.cirrus.com
Reviewed-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Mark Brown <broonie@kernel.org>