Add dummy function for swrm_wcd_notify to avoid
compilation errors when configuration options
'CONFIG_SOUNDWIRE' and 'CONFIG_SOUNDWIRE_WCD_CTRL'
are not selected for a target.
Change-Id: Ie12d2df8777934494f0f8607d846e2d1ec49f2a6
Signed-off-by: Xiaoyu Ye <benyxy@codeaurora.org>