speakup: fix incorrect perms on speakup_acntsa.c

22c9bcad contained a bad
substitution for ROOT_W => S_IRUSR|S_IRUGO instead of
S_IWUSR|S_IRUGO.

Fixes: 22c9bcad
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>