staging: speakup: speakup_soft.c: style fixes

* Clean this file based on reports from checkpatch.pl.
* Make the file_operations structure const.
* Use strict_strtoul instead of simple_strtoul.

Signed-off-by: Christopher Brannon <chris@the-brannons.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>