sonic: replace divide() by ROUNDED_DIV()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
sonic: cleanup/simplify num_taps check

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
sonic: use av_freep() as its safer than av_free()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>