aacsbr: optimize sine level addition

Based-on commit by Måns Rullgård <mans@mansr.com>

original:   1424 decicycles in phi, 1024 runs, 0 skips
mans code:  1104 decicycles in phi, 1024 runs, 0 skips
this change: 734 decicycles in phi, 1024 runs, 0 skips

mans code:   1 file changed, 20 insertions(+), 10 deletions(-)
this change: 1 file changed, 10 insertions(+), 6 deletions(-)

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