This means that as of this commit, the signal has to be permanently
regenerated. In fact, with the SRS queue to be introduced in a follow-up
commit, we don't have an easy way to cache the sequence generation, as
there is no "index" to which we could refer to (hence, caching would be
tricky).

Instead, the next commits further refactor this to reduce the time for
SRS sequence generation as well as the memory footprint.
Signed-off-by: Robert Schmidt <robert.schmidt@openairinterface.org>