The difference between an EF-s lens and an EF lens is only that an EF-s lens does not project a big enough image circle to cover a full frame and may stick too far in to the camera body to be used safely with full frame cameras.
The focal length is a measure of a physical property of the lens rather than having anything to do with the size of the sensor. We simply refer to an APS-c sensor as being a crop sensor because the 35mm film format was decided as the value for a crop factor of 1.
A 24mm photo is still a 24mm photo regardless of if you take it on an APS-c or a full frame or even a large format camera. The only difference is that the portion of the projected image that is captured is smaller due to the smaller sensor area that is exposed, thus it would require a longer focal length to get an equivalent angle of view from a larger sensor.