Add missing \returns, change "return" to "returns" to have same naming

include/SDL3/SDL_metal.h

@@ -58,6 +58,8 @@ typedef void *SDL_MetalView;
  * The returned handle can be casted directly to a NSView or UIView. To access
  * the backing CAMetalLayer, call SDL_Metal_GetLayer().
  *
+ * \returns handle NSView or UIView
+ *
  * \since This function is available since SDL 3.0.0.
  *
  * \sa SDL_Metal_DestroyView
@@ -80,6 +82,8 @@ extern DECLSPEC void SDLCALL SDL_Metal_DestroyView(SDL_MetalView view);
 /**
  * Get a pointer to the backing CAMetalLayer for the given view.
  *
+ * \returns a pointer
+ *
  * \since This function is available since SDL 3.0.0.
  *
  * \sa SDL_Metal_CreateView