Shrink the {in,out}put_source arrays and their data type to what is
actually necessary.

To be still on the safe side, add some static asserts.
Signed-off-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
Link: https://lore.kernel.org/r/20230516093612.3536508-11-oswald.buddenhagen@gmx.deSigned-off-by: Takashi Iwai <tiwai@suse.de>