Fix interpolator

If the phase increment was larger than the loop size, the interpolator
would read further and further outside the sample, eventually segfaulting.

Bug: 38342499
Test: manual
Change-Id: I0e70d037e61fdeffdbd49460caa692e9781cc511
(cherry picked from commit d19edc9c090d64926469463991ca7e86c73368fa)