egl: Fix -Wint-to-pointer-cast

egl: Fix -Wint-to-pointer-cast

main/egldisplay.c: In function '_eglParseX11DisplayAttribList':
main/egldisplay.c:491:38: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
          display->Options.Platform = (void *)value;

The fix: cast to uinptr_t before void*.
                                      ^
Fixes: ddb99127 egl/x11: Honor the EGL_PLATFORM_X11_SCREEN_EXT attribute
Cc: Adam Jackson <ajax@redhat.com>
Reviewed-by: Eric Engestrom <eric@engestrom.ch>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>