staging: speakup: speakup_decext.c: style fixes

* Clean this file based on reports from checkpatch.pl.
* Replace function-like macros with inline macros.
* Eliminate a use of the ternary operator, for readability.

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