staging/lynxfb: Use pci aperture helper

It exists! Note that since this is an exact copy, there shouldn't be
any functional difference here.

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Cc: Teddy Wang <teddy.wang@siliconmotion.com>
Cc: linux-fbdev@vger.kernel.org
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20230111154112.90575-6-daniel.vetter@ffwll.ch