V4L/DVB (6830): cx88-blackbird: remove unnecessary encoder unmute

Remove the unnecessary BLACKBIRD_UNMUTE calls to the mpeg encoder in
cx88-blackbird.c

The encoder is never muted, hence unmuting should then only be necessary
once after hardware initialization.

I tested this from warm boots and cold boots (with long power down time
to ensure the sram in the chip is emptied), and found that after the
firmware upload the encoder is apparently not muted, making the unmutes
unnecessary.

Signed-off-by: Jelle Foks <jelle@foks.8m.com>
Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>