The userland callers are responsible for clearing the output buffers, so
remove the unneeded memset calls.

Thanks to Mauro Carvalho Chehab <mchehab@infradead.org> for pointing this out.
Signed-off-by: Devin Heitmueller <dheitmueller@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>