soundwire: Fix DEBUG_LOCKS_WARN_ON for uninitialized attribute

running kernel with CONFIG_DEBUG_LOCKS_ALLOC enabled will below warning:

BUG: key ffff502e09807098 has not been registered!
DEBUG_LOCKS_WARN_ON(1)
WARNING: CPU: 5 PID: 129 at kernel/locking/lockdep.c:4623
	lockdep_init_map_waits+0xe8/0x250
Modules linked in:
CPU: 5 PID: 129 Comm: kworker/5:1 Tainted: G
       W         5.10.0-rc1-00277-ged49f224ca3f-dirty #1210
Hardware name: Qualcomm Technologies, Inc. Robotics RB5 (DT)
Workqueue: events deferred_probe_work_func
pstate: 80c00005 (Nzcv daif +PAN +UAO -TCO BTYPE=--)
pc : lockdep_init_map_waits+0xe8/0x250
lr : lockdep_init_map_waits+0xe8/0x250
 [ Trimmed ]

Call trace:
 lockdep_init_map_waits+0xe8/0x250
 __kernfs_create_file+0x78/0x180
 sysfs_add_file_mode_ns+0x94/0x1c8
 internal_create_group+0x110/0x3e0
 sysfs_create_group+0x18/0x28
 devm_device_add_group+0x4c/0xb0
 add_all_attributes+0x438/0x490
 sdw_slave_sysfs_dpn_init+0x128/0x138
 sdw_slave_sysfs_init+0x80/0xa0
 sdw_drv_probe+0x94/0x170
 really_probe+0x118/0x3e0
 driver_probe_device+0x5c/0xc0

 [ Trimmed ]

CPU: 5 PID: 129 Comm: kworker/5:1 Tainted: G
     W         5.10.0-rc1-00277-ged49f224ca3f-dirty #1210
Hardware name: Qualcomm Technologies, Inc. Robotics RB5 (DT)
Workqueue: events deferred_probe_work_func
Call trace:
 dump_backtrace+0x0/0x1c0
 show_stack+0x18/0x68
 dump_stack+0xd8/0x134
 __warn+0xa0/0x158
 report_bug+0xc8/0x178
 bug_handler+0x20/0x78
 brk_handler+0x70/0xc8

[ Trimmed ]

Fix this by initializing dynamically allocated sysfs attribute to keep lockdep happy!

Fixes: bcac590299 ("soundwire: add Slave sysfs support")
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Acked-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20201104112941.1134-1-srinivas.kandagatla@linaro.org
Signed-off-by: Vinod Koul <vkoul@kernel.org>

drivers/soundwire/sysfs_slave_dpn.c

@@ -37,6 +37,7 @@ static int field##_attribute_alloc(struct device *dev,			\
 		return -ENOMEM;						\
 	dpn_attr->N = N;						\
 	dpn_attr->dir = dir;						\
+	sysfs_attr_init(&dpn_attr->dev_attr.attr);			\
 	dpn_attr->format_string = format_string;			\
 	dpn_attr->dev_attr.attr.name = __stringify(field);		\
 	dpn_attr->dev_attr.attr.mode = 0444;				\