The src buffer should only contain values in the interval
[0, (1 << BIT_DEPTH) - 1]. Since shift = (BIT_DEPTH - 5), src[x] >> shift
must be in the interval [0, 31], so no clip is needed.

This removes the code that was changed in 5856bca3
as the clip that was repositioned in that commit is removed
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>