fix helix/rev2:edvorakjp build error (#16433)

'helix/rev2/keymaps/edvorakjp' was no longer buildable due to changes made by #14864.
The reason is that the prototype of `oled_task_user()` was changed in keymaps/edvorakjp/oled.c, but keymaps/edvorakjp/oled.h was not changed.
Therefore, I modified the prototype in keymaps/edvorakjp/oled.h.

keyboards/helix/rev2/keymaps/edvorakjp/oled.h

@@ -9,4 +9,4 @@ void            render_layer_state(void);
 void            render_logo(void);
 void            render_mode_icon(bool is_windows);
 oled_rotation_t oled_init_user(oled_rotation_t rotation);
-void            oled_task_user(void);
+bool            oled_task_user(void);