Staging: speakup: Replace symbolic permission

Replace S_IRUGO by 0444 in module parameter declaration. 0444 is more
readable and matches the style used in other declarations nearby.

Problem found using checkpatch.

Signed-off-by: Meghana Madhyastha <meghana.madhyastha@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>