Fix the problem that the range check for scalar narrow shift is too wide.
E.g. the immediate value of vshrns_n_s16 is [1,16], which should be [1,8].


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@195942 91177308-0d34-0410-b5e6-96231b3b80d8