regulator: core: use system_freezable_wq for init complete work

schedule_delayed_work() uses system_wq, which is non-freezable, allowing
regulator_init_complete_work to run concurrently with system suspend. This
work fires ~30s after boot to disable unused regulators via I2C. When it
races with PM suspend, the I2C adapter may already be suspended, triggering
a -ESHUTDOWN warning in __i2c_transfer():

  WARNING: ... at __i2c_transfer+0x36c/0x3c8
  Call trace:
   __i2c_transfer
   i2c_transfer
   regmap_i2c_write
   _regmap_update_bits
   regulator_disable_regmap
   _regulator_do_disable
   regulator_late_cleanup
   regulator_init_complete_work_function
   process_one_work

Switch to system_freezable_wq so the work is frozen before any device
is suspended, eliminating the race.

Fixes: 55576cf185 ("regulator: Defer init completion for a while after late_initcall")
Signed-off-by: Joy Zou <joy.zou@oss.nxp.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Link: https://patch.msgid.link/20260731-b4-regulator-pf01-v2-1-a406c8737fdb@oss.nxp.com
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/regulator/core.c

@@ -27,6 +27,7 @@
 #include <linux/regulator/driver.h>
 #include <linux/regulator/machine.h>
 #include <linux/module.h>
+#include <linux/workqueue.h>
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/regulator.h>
@@ -6899,8 +6900,9 @@ static int __init regulator_init_complete(void)
 	 * we'd only do this on systems that need it, and a kernel
 	 * command line option might be useful.
 	 */
-	schedule_delayed_work(&regulator_init_complete_work,
-			      msecs_to_jiffies(30000));
+	queue_delayed_work(system_freezable_wq,
+			   &regulator_init_complete_work,
+			   msecs_to_jiffies(30000));
 
 	return 0;
 }