soundwire: intel: fix missing assignment to ret

Currently the return status ret is being checked but it has not been
updated since the previous check on ret. It appears that assignment of
ret from return status of the call to sdw_cdns_enable_interrupt was
accidentally ommited.  Fix this.

Detected by CoverityScan, CID#1463148 ("Logically dead code")

Fixes: 71bb8a1b ("soundwire: intel: Add Intel Master driver")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>