Fix return value of gpio::ReadPin

The cast to Level is incorrect, since the expression returns either 0 or
a positive value if the pin is set. The value is directly assigned to
the underlying uint8_t, meaning that Level::high won't match for levels
greater than 0.

Return a boolean and cast that to Level instead.

src/hal/gpio.h

@@ -57,7 +57,7 @@ __attribute__((always_inline)) inline void WritePin(const GPIO_pin portPin, Leve
 }
 
 __attribute__((always_inline)) inline Level ReadPin(const GPIO_pin portPin) {
-    return (Level)(portPin.port->PINx & (1 << portPin.pin));
+    return (Level)((portPin.port->PINx & (1 << portPin.pin)) != 0);
 }
 
 __attribute__((always_inline)) inline void TogglePin(const GPIO_pin portPin) {