staging: speakup: speakup_dtlk.c: style fixes

* Clean this file based on reports from checkpatch.pl.
* Replace function-like macros with inline functions.
* Simplify some boolean expressions.

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