gamecontroller: Fix function name in cherry-picked documentation

SDL_GetGamepadAxis() is a SDL3-specific name: SDL2 calls gamepads
"game controllers".

Fixes: d3c21666 "gamepad: Clarify range and direction of axes"
Signed-off-by: Simon McVittie <smcv@collabora.com>

include/SDL_gamecontroller.h

@@ -614,7 +614,7 @@ extern DECLSPEC void SDLCALL SDL_GameControllerUpdate(void);
  *  or autodetect the dead zone, which varies between controllers.
  *
  *  Trigger axis values range from 0 (released) to SDL_JOYSTICK_AXIS_MAX
- *  (fully pressed) when reported by SDL_GetGamepadAxis(). Note that this is not the
+ *  (fully pressed) when reported by SDL_GameControllerGetAxis(). Note that this is not the
  *  same range that will be reported by the lower-level SDL_GetJoystickAxis().
  */
 typedef enum