ARM: shmobile: rcar-gen2: Fix deadlock in regulator quirk

Simon Horman reported that Koelsch and Lager hang during boot, and
bisected this to commit 1c3c5ea ("sched/core: Enable
might_sleep() and smp_processor_id() checks early").

The da9063/da9210 regulator quirk for R-Car Gen2 boards uses a bus
notifier, and unregisters the notifier when it is no longer needed.
However, a notifier must not be unregistered from within the call chain.

This bug went unnoticed, as blocking_notifier_chain_unregister() didn't
take the semaphore during early boot.  The aforementioned commit changed
that behavior, leading to a deadlock.

Fix this by removing the call to bus_unregister_notifier(), and keeping
local completion state instead.

Reported-by: Simon Horman <horms+renesas@verge.net.au>
Fixes: 663fbb5 ("ARM: shmobile: R-Car Gen2: Add da9063/da9210 regulator quirk")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>

arch/arm/mach-shmobile/regulator-quirk-rcar-gen2.c

@@ -67,8 +67,12 @@ static int regulator_quirk_notify(struct notifier_block *nb,
 {
 	struct device *dev = data;
 	struct i2c_client *client;
+	static bool done;
 	u32 mon;
 
+	if (done)
+		return 0;
+
 	mon = ioread32(irqc + IRQC_MONITOR);
 	dev_dbg(dev, "%s: %ld, IRQC_MONITOR = 0x%x\n", __func__, action, mon);
 	if (mon & REGULATOR_IRQ_MASK)
@@ -99,7 +103,7 @@ static int regulator_quirk_notify(struct notifier_block *nb,
 remove:
 	dev_info(dev, "IRQ2 is not asserted, removing quirk\n");
 
-	bus_unregister_notifier(&i2c_bus_type, nb);
+	done = true;
 	iounmap(irqc);
 	return 0;
 }