regulator: avoid resolve_supply() infinite recursion

When a regulator's name equals its supply's name the
regulator_resolve_supply() recurses indefinitely. Add a check
so that debugging the problem is easier. The "fixed" commit
just exposed the problem.

Fixes: aea6cb9 ("regulator: resolve supply after creating regulator")
Cc: stable@vger.kernel.org
Reported-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Tested-by: Ahmad Fatoum <a.fatoum@pengutronix.de> # stpmic1
Link: https://lore.kernel.org/r/c6171057cfc0896f950c4d8cb82df0f9f1b89ad9.1605226675.git.mirq-linux@rere.qmqm.pl
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/regulator/core.c

@@ -1841,6 +1841,12 @@ static int regulator_resolve_supply(struct regulator_dev *rdev)
 		}
 	}
 
+	if (r == rdev) {
+		dev_err(dev, "Supply for %s (%s) resolved to itself\n",
+			rdev->desc->name, rdev->supply_name);
+		return -EINVAL;
+	}
+
 	/*
 	 * If the supply's parent device is not the same as the
 	 * regulator's parent device, then ensure the parent device