Prevent NULL dereference if kzalloc() fails.

Cc: Devin Heitmueller <dheitmueller@linuxtv.org>
Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Signed-off-by: Douglas Schilling Landgraf <dougsland@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>