staging: speakup: Use octal permissions '0444'

Fixed the following checkpatch warning:

WARNING: Symbolic permissions 'S_IRUGO' are not preferred. Consider using octal
permissions '0444'.

Signed-off-by: Mihaela Muraru <mihaela.muraru21@gmail.com>
Acked-by: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>