helpers: media_device: ignore lockf return value

When using gcc (with ~-Werror=unused-result), compilation fails,
because the return value of lockf is ignored at one place.

To avoid this error, assign the return value to std::ignore.

Signed-off-by: Gyorgy Sarvari <[email protected]>

Author: OldManYellsAtCloud

src/helpers/media_device.cpp

@@ -248,6 +248,6 @@ std::map<std::string, DeviceFd>::iterator MediaDevice::unlock(const std::string
 	if (it == lock_map_.end())
 		return lock_map_.end();
 
-	lockf(it->second.Get(), F_ULOCK, 0);
+	std::ignore = lockf(it->second.Get(), F_ULOCK, 0);
 	return lock_map_.erase(it);
 }