staging: dgap: uses kzalloc for allocating memory

Originally, this driver created it's own allocating
function. This patch removes that function and calls
kzalloc directly.

This patch affects:
 - driver.c
 - driver.h
 - fep5.c
 - tty.c

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