media: si2157: Briefly wait for tuning operation to complete

To detect errors in the tuning operation, this waits up 40ms for operation
completion status. This allows for error detection and prevents issuing
additional commands to the tuner before it is finished.

Tuning typically completes in 20-30ms.

Signed-off-by: Brad Love <brad@nextdimension.cc>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>