fix linux_pwm_out: return correct value for PCA9685::init()

src/drivers/linux_pwm_out/PCA9685.h

@@ -82,7 +82,7 @@ public:
 	 */
 	PCA9685(int bus, int address);
 
-	int init() override { return _fd >= 0; }
+	int init() override { return _fd >= 0 ? 0 : -1; }
 
 	int send_output_pwm(const uint16_t *pwm, int num_outputs) override;
 

src/drivers/linux_pwm_out/linux_pwm_out.cpp

@@ -217,13 +217,7 @@ void task_main(int argc, char *argv[])
 		pwm_out = new NavioSysfsPWMOut(_device, _max_num_outputs);
 	}
 
-	/**
-	 * if the _protocol is "pca9685" and the driver is executed correctly，
-	 * the return value of "pwm_out->init()" will be higher than 0.
-	 */
-	bool check_pwm_device = (strcmp(_protocol, "pca9685") == 0) ? (0 > pwm_out->init()) : (pwm_out->init() != 0);
-
-	if (check_pwm_device) {
+	if (pwm_out->init() != 0) {
 		PX4_ERR("PWM output init failed");
 		delete pwm_out;
 		return;