soundwire: slave: use SDW_DISCO_LINK_ID()

use SDW_DISCO_LINK_ID() in slave code to extract field values instead of
open coding masks and shift operations to extract link_id

Signed-off-by: Vinod Koul <vkoul@kernel.org>
Tested-by: Bard Liao <yung-chuan.liao@linux.intel.com>
Link: https://lore.kernel.org/r/20200903114504.1202143-4-vkoul@kernel.org


Signed-off-by: Vinod Koul <vkoul@kernel.org>