V4L/DVB: DVB: ngene, fix memset parameters

Switch second and third memset parameter to stamp the length buffer bytes
by 0xff's, not 255 bytes by low 8 bits of Length.

Cc: linux-media@vger.kernel.org, linux-kernel@vger.kernel.org, 	jirislaby@gmail.com, Matthias Benesch <twoof7@freenet.de>, 	Ralph Metzler <rjkm@metzlerbros.de>, Oliver Endriss <o.endriss@gmx.de>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Matthias Benesch <twoof7@freenet.de>
Cc: Ralph Metzler <rjkm@metzlerbros.de>
Cc: Oliver Endriss <o.endriss@gmx.de>
Cc: Mauro Carvalho Chehab <mchehab@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>