Prevent NULL dereference if kzalloc() fails.

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