ir: clock: use value in cycles instead of ns

ir: clock: use value in cycles instead of ns

The value of a clock in CTF is in cycles, not in nanoseconds.
Here, bt_ctf_clock_get_time() and bt_ctf_clock_set_time() are left
as utilities to converter from/to the clock value in cycles.
Note that this conversion, unless the frequency is exactly 1 GHz,
implies casting 64-bit integers to doubles so it is possible to
lose accuracy.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>