soundwire: bus: stop dereferencing invalid slave pointer

Slave pointer is invalid after end of list iteration, using this
would result in below Memory abort.

Unable to handle kernel NULL pointer dereference at virtual address 0000000000000004
...
Call trace:
 __dev_printk+0x34/0x7c
 _dev_warn+0x6c/0x90
 sdw_bus_exit_clk_stop+0x194/0x1d0
 swrm_runtime_resume+0x13c/0x238
 pm_generic_runtime_resume+0x2c/0x48
 __rpm_callback+0x44/0x150
 rpm_callback+0x6c/0x78
 rpm_resume+0x314/0x558
 rpm_resume+0x378/0x558
 rpm_resume+0x378/0x558
 __pm_runtime_resume+0x3c/0x88

Use bus->dev instead to print this error message.

Fixes: b50bb8ba36 ("soundwire: bus: handle -ENODATA errors in clock stop/start sequences")
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20211012101521.32087-1-srinivas.kandagatla@linaro.org
Signed-off-by: Vinod Koul <vkoul@kernel.org>

drivers/soundwire/bus.c

@@ -1110,7 +1110,7 @@ int sdw_bus_exit_clk_stop(struct sdw_bus *bus)
 	if (!simple_clk_stop) {
 		ret = sdw_bus_wait_for_clk_prep_deprep(bus, SDW_BROADCAST_DEV_NUM);
 		if (ret < 0)
-			dev_warn(&slave->dev, "clock stop deprepare wait failed:%d\n", ret);
+			dev_warn(bus->dev, "clock stop deprepare wait failed:%d\n", ret);
 	}
 
 	list_for_each_entry(slave, &bus->slaves, node) {