rtlsdr_demod_write_reg(): return 0 on success

Thanks to DreamNik for reporting this issue.

Signed-off-by: Steve Markgraf <steve@steve-m.de>

src/librtlsdr.c

@@ -452,7 +452,7 @@ int rtlsdr_demod_write_reg(rtlsdr_dev_t *dev, uint8_t page, uint16_t addr, uint1
 
 	rtlsdr_demod_read_reg(dev, 0x0a, 0x01, 1);
 
-	return r;
+	return (r == len) ? 0 : -1;
 }
 
 void rtlsdr_set_gpio_bit(rtlsdr_dev_t *dev, uint8_t gpio, int val)