staging: gdm724x: kzalloc should be used instead of kmalloc/memset

This patch fixes the following coccinelle warnings in driver gdm724x:

drivers/staging/gdm724x/gdm_usb.c:127:9-16: WARNING: kzalloc should be used for t_sdu, instead of kmalloc/memset
drivers/staging/gdm724x/gdm_usb.c:91:5-12: WARNING: kzalloc should be used for t, instead of kmalloc/memset

Signed-off-by: Teodora Baluta <teobaluta@gmail.com>
Reviewed-by: Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>