V4L/DVB (7572): mt312: Fix diseqc

Correct the frequency of the emitted diseqc signal to 22kHz.
Adds sleep(100) to wait for message to be transmitted.

For now the only user of mt312 is b2c2-flexcop, and it
does overwrite all diseqc related functions with own code.

Signed-off-by: Matthias Schwarzott <zzam@gentoo.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>