Original code for 'DoubleOhThree' encoding was written with '__u8' type,
while the type is usually used to export something to userspace.

This commit replaces the type with 'u8'.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>