Fixed undefined behaviour left shifting a negative integer

clang's ubsan complained:
Common/DataModel/vtkPerlinNoise.cxx:39:9: runtime error: left shift of negative value -394

when running the PerlinNoise tests. Most/all compilers generate code
that does what you might expect (treat it as unsigned), so I just changed
the function to take an unsigned value. I verified that the results are
identical (with clang anyway).

Change-Id: I472c1983bf66c2ab90887ed531c482fcf1ab5aed
Merge topic 'sanitize-shift' into master

c1bbf8de Fixed undefined behaviour left shifting a negative integer