speakup: lower default software speech rate

Speech synthesis beginners need a low speech rate, and trained people
want a high speech rate.  A medium speech rate is thus actually not a
good default for neither.  Since trained people will typically know how
to change the rate, better default for a low speech rate, which
beginners can grasp and learn how to increase it afterwards

This was agreed with users on the speakup mailing list.

Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>