[Issue-Fix #697] Fixes ltv crash issue due to st->cngTDLevel_e coming greater than 15

[x] The crash occurs due to st->cngTDLevel_e coming greater
than 15, which was leading to -ve Q which was not handled by
fix16_to_float() while converting st->cngTDLevel to
st->cngTDLevel_float.
[x] Used fixedToFloat() instead of fix16_to_float() which
is able to handle -ve Q.