avcodec/adxdec: Remove unnecessary left-shift

Replace "(a * (1 << shift) * b + c) >> shift" by "a * b + (c >> shift)".
It is equivalent to the old code because a is in the range of uint16_t,
shift is 12 and b is effectively a signed 4-bit number, so that no
overflow/truncation of high bits happens during the multiplication
(overflow would be undefined anyway).
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/adxdec.c

@@ -81,7 +81,7 @@ static int adx_decode(ADXContext *c, int16_t *out, int offset,
     s2 = prev->s2;
     for (i = 0; i < BLOCK_SAMPLES; i++) {
         d  = get_sbits(&gb, 4);
-        s0 = ((d * (1 << COEFF_BITS)) * scale + c->coeff[0] * s1 + c->coeff[1] * s2) >> COEFF_BITS;
+        s0 = d * scale + ((c->coeff[0] * s1 + c->coeff[1] * s2) >> COEFF_BITS);
         s2 = s1;
         s1 = av_clip_int16(s0);
         *out++ = s1;