staging: speakup: fix unnecessary long line

Fix checkpatch message:
WARNING: line over 80 characters

Change "bit mask" for "bitmask" to have a line shorter than 80 characters.

Signed-off-by: Michael Mera <dev@michaelmera.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>