Fix another build error.

tests/ColorTests/UnitTest/color_mock_libuvc.cpp

@@ -19,7 +19,7 @@ static int g_device_ref_count = 0;
 static uint8_t g_ae_mode = 8; // default is UVC_AUTO_EXPOSURE_MODE_APERTURE_PRIORITY
 static uint32_t g_exposure_abs = 127;
 static uint8_t g_ae_priority = 1;
-static uint16_t g_brightness = 128;
+static int16_t g_brightness = 128;
 static uint16_t g_contrast = 5;
 static uint16_t g_saturation = 32;
 static uint16_t g_sharpness = 2;