soundwire: remove bitfield for unique_id, use u8

There is no good reason why the unique_id needs to be stored as 4
bits. The code will work without changes with a u8 since all values
are already filtered while parsing the ACPI tables and Slave devID
registers.

Use u8 representation. This will allow us to encode a
"IGNORE_UNIQUE_ID" value to account for firmware/BIOS creativity.
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20191022234808.17432-2-pierre-louis.bossart@linux.intel.comSigned-off-by: Vinod Koul <vkoul@kernel.org>

include/linux/soundwire/sdw.h

@@ -403,6 +403,8 @@ int sdw_slave_read_prop(struct sdw_slave *slave);
  * SDW Slave Structures and APIs
  */
 
+#define SDW_IGNORED_UNIQUE_ID 0xFF
+
 /**
  * struct sdw_slave_id - Slave ID
  * @mfg_id: MIPI Manufacturer ID
@@ -418,7 +420,7 @@ struct sdw_slave_id {
 	__u16 mfg_id;
 	__u16 part_id;
 	__u8 class_id;
-	__u8 unique_id:4;
+	__u8 unique_id;
 	__u8 sdw_version:4;
 };