media: ttusb-dec: Fix info-leak in ttusb_dec_send_command()

The function at issue does not always initialize each byte allocated
for 'b' and can therefore leak uninitialized memory to a USB device in
the call to usb_bulk_msg()

Use kzalloc() instead of kmalloc()

Signed-off-by: Tomas Bortoli <tomasbortoli@gmail.com>
Reported-by:  <syzbot+0522702e9d67142379f1@syzkaller.appspotmail.com>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>