speakup: Fix building as extmod

spk_priv_keyinfo.h should be opened from the speakup directory. When
building as extmod we should thus open it from the module directory
rather than the main Linux source.

Signed-off-by: Samuel <Thibault &lt;samuel.thibault@ens-lyon.org>
Link: https://lore.kernel.org/r/20221118012206.j6hq6b6nfx2jhqg6@begin


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>