[SPIR-V] Crash when using sampler on half texture

[Keenuts]

Description

DXC crashes when Sample is used on a texture storing 16bit floats.

Steps to Reproduce

// RUN: %dxc -T cs_6_7 -E main -spirv -enable-16bit-types %s | FileCheck %s

Texture2D<half> texture;
RWBuffer<half> buffer;
SamplerState s;

[numthreads(8, 8, 8)]
void main() {
  half t = texture.Sample(s, float2(0, 0));
}

Actual Behavior

DirectXShaderCompiler/tools/clang/lib/SPIRV/LowerTypeVisitor.cpp(186)
Func:	visitInstruction