ASoC: SOF: imx: add header file for ops

Sparse (make C=2) complains about undeclared variables. Fix by adding
a real prototype instead of 'extern' in sof-of-dev.c

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Reviewed-by: Daniel Baluta <daniel.baluta@gmail.com>
Reviewed-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>
Reviewed-by: Paul Olaru <paul.olaru@oss.nxp.com>
Signed-off-by: Peter Ujfalusi <peter.ujfalusi@linux.intel.com>
Link: https://lore.kernel.org/r/20210928072807.27838-1-peter.ujfalusi@linux.intel.com


Signed-off-by: Mark Brown <broonie@kernel.org>