spirv-val: Fix comment for checking extended alignments (#4937)
spirv-val: Fix comment for checking extended alignments (#4937)

* getBaseAlignment with roundUp true is called the "extended"
  by the Vulka spec.
* roundUp also affects matrix alignment, not just struct and array
KhronosGroup/SPIRV-Tools,KhronosGroup/SPIRV-Tools,KhronosGroup/SPIRV-Tools,KhronosGroup/SPIRV-Tools,KhronosGroup/SPIRV-Tools,KhronosGroup/SPIRV-Tools,KhronosGroup/SPIRV-Tools,KhronosGroup/SPIRV-Tools