soundwire: bus: fix off-by-one when allocating slave IDs

ida_alloc_max() interprets its max argument as inclusive.

Using SDW_FW_MAX_DEVICES(16) therefore allows an ID of 16 to be
allocated, but the IRQ domain created for the bus is sized for IDs
0-15.  If 16 is returned, irq_create_mapping() fails and the driver
ends up with an invalid IRQ mapping.

Limit the allocation to 0-15 by passing SDW_FW_MAX_DEVICES - 1.

Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/r/202512240450.hlDH3nCs-lkp@intel.com/
Fixes: aab1202 ("soundwire: bus: Add internal slave ID and use for IRQs")
Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>
Reviewed-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Link: https://patch.msgid.link/20260110201959.2523024-1-harshit.m.mogalapalli@oracle.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

Author: harshimogalapalli

drivers/soundwire/bus_type.c

@@ -105,7 +105,7 @@ static int sdw_drv_probe(struct device *dev)
 	if (ret)
 		return ret;
 
-	ret = ida_alloc_max(&slave->bus->slave_ida, SDW_FW_MAX_DEVICES, GFP_KERNEL);
+	ret = ida_alloc_max(&slave->bus->slave_ida, SDW_FW_MAX_DEVICES - 1, GFP_KERNEL);
 	if (ret < 0) {
 		dev_err(dev, "Failed to allocated ID: %d\n", ret);
 		return ret;