staging: dgnc: driver.c and tty.c: replaces dgnc_driver_kzmalloc with kzalloc

This patch replaces dgnc_driver_kzmalloc with kzalloc.
A patch that follows removes the dgnc_driver_kzmalloc
function.

Signed-off-by: Lidza Louina <lidza.louina@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>