soundwire: Intel: test bus.bpt_stream before assigning it

soundwire: Intel: test bus.bpt_stream before assigning it

We only allow up to 1 bpt stream running on a SoundWire bus.
bus.bpt_stream will be assigned when it is opened and will be set to
NULL when it is closed. We do check bus->bpt_stream_refcount if the
stream type is SDW_STREAM_BPT in sdw_master_rt_alloc(), but at that
moment the bpt stream is allocated and set to bus.bpt_stream. It will
lead to the original bus.bpt_stream be changed to the new and not used
bpt stream. And it will be released and set to NULL when
sdw_slave_bpt_stream_add() return error as it supposed to. Then the
original stream will try to use the NULL bus.bpt_stream.

Fixes: 4c1ce9f37d8a ("soundwire: intel_ace2x: add BPT send_async/wait callbacks")
Reported-by: Simon Trimmer <simont@opensource.cirrus.com>
Signed-off-by: Bard Liao <yung-chuan.liao@linux.intel.com>
Reviewed-by: Simon Trimmer <simont@opensource.cirrus.com>
Reviewed-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
Link: https://patch.msgid.link/20260126054045.2504103-1-yung-chuan.liao@linux.intel.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>