soundwire: bus: Simplify sdw_assign_device_num()

Simplify the code in sdw_assign_device_num(). Remove the new_device
flag which can be simply handled inline and do a bit less shuffling of
dev_num in and out of various variables. This patch should cause no
functional changes.

Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.dev>
Link: https://lore.kernel.org/r/20250429101808.348462-2-ckeepax@opensource.cirrus.com


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