regulator: core: fix use_count leakage when handling boot-on

I found a use_count leakage towards supply regulator of rdev with
boot-on option.

┌───────────────────┐           ┌───────────────────┐
│  regulator_dev A  │           │  regulator_dev B  │
│     (boot-on)     │           │     (boot-on)     │
│    use_count=0    │◀──supply──│    use_count=1    │
│                   │           │                   │
└───────────────────┘           └───────────────────┘

In case of rdev(A) configured with `regulator-boot-on', the use_count
of supplying regulator(B) will increment inside
regulator_enable(rdev->supply).

Thus, B will acts like always-on, and further balanced
regulator_enable/disable cannot actually disable it anymore.

However, B was also configured with `regulator-boot-on', we wish it
could be disabled afterwards.

Signed-off-by: Rui Zhang <zr.zhang@vivo.com>
Link: https://lore.kernel.org/r/20221201033806.2567812-1-zr.zhang@vivo.com
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: Rui Zhang

drivers/regulator/core.c

@@ -1596,7 +1596,13 @@ static int set_machine_constraints(struct regulator_dev *rdev)
 		if (rdev->supply_name && !rdev->supply)
 			return -EPROBE_DEFER;
 
-		if (rdev->supply) {
+		/* If supplying regulator has already been enabled,
+		 * it's not intended to have use_count increment
+		 * when rdev is only boot-on.
+		 */
+		if (rdev->supply &&
+		    (rdev->constraints->always_on ||
+		     !regulator_is_enabled(rdev->supply))) {
 			ret = regulator_enable(rdev->supply);
 			if (ret < 0) {
 				_regulator_put(rdev->supply);