V4L/DVB (9397): fix some bugs at tda8261

Fix bug obviously, some enhancements as well

* enable i2c_gate before doing any transaction
* read is one single message with 2 words
* reduce sleep from 100mS to 20mS

Signed-off-by: Manu Abraham <manu@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>