gpio: bcm-virt: Fix the get() method

The get() method does not understand the on-the-wire encoding of the
remote GPIO states, thinking they are simple on/off bits when they are
really pairs of 16-bit counts. Rewrite the get() handler to return the
value last written, which will eventually match the actual GPIO state
if there are no other changes.

See: #4638

Signed-off-by: Phil Elwell <phil@raspberrypi.com>

drivers/gpio/gpio-bcm-virt.c

@@ -49,7 +49,7 @@ static int brcmvirt_gpio_get(struct gpio_chip *gc, unsigned off)
 	unsigned v;
 	gpio = container_of(gc, struct brcmvirt_gpio, gc);
 	v = readl(gpio->ts_base + off);
-	return (v >> off) & 1;
+	return (s16)((v >> 16) - v) > 0;
 }
 
 static void brcmvirt_gpio_set(struct gpio_chip *gc, unsigned off, int val)