V4L/DVB (3971): Cx88-blackbird: use standard filename for cx23416 firmware

cx88-blackbird uses the same encoder firmware for the cx23416 chip that is
used by ivtv and pvrusb2.
This patch alters the driver to expect the cx23416 encoder firmware to be
located in the file, "v4l-cx2341x-enc.fw", instead of using
"blackbird-fw-enc.bin"

Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>