dvbsrc: improve timeout handing at locking loop

The previous approach was too much of an aproximation
by considering each polling round took roughly the
step timeout itself. This approach attempts to be
more accurate by actually measuring the elapsed time.
Additionally, we now use a 10 seconds default timeout
for the tuning/locking logic and a half a second
polling step. These values should better delimit the
tuning process on real-life scenarios.

This patch also adds _retry_ioctl() to avoid bailing
out on temporary ioctl EINTR failures (no need to
check for EAGAIN cause we are opening the frontend on
blocking mode) and starts using it for the tuning/locking
routine.
dvbsrc: drop redundant assignment
dvbsrc: add Samsung copyright attribution