drivers/staging: refactor dgnc tty registration.

-remove duplicate tty allocation code for serial and printer drivers.
-add missing tty c_ispeed and c_ospeed initialization to 9600.
-fix sparse warning: too long initializer-string for array of char.

This patch was only unit tested due to lack of the actual hardware.

Signed-off-by: Haim Daniel <haimdaniel@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>