[AMDGPU] Use correct vector elt type when shrinking mfma scale (#123043)

This might be a copy/paste error. I don't think this an issue in
practice as the builtins/intrinsics are only legal with identical vector
element types.

Author: frasercrmck

llvm/lib/Target/AMDGPU/AMDGPUInstCombineIntrinsic.cpp

@@ -1346,7 +1346,7 @@ GCNTTIImpl::instCombineIntrinsic(InstCombiner &IC, IntrinsicInst &II) const {
 
     if (Src1Ty->getNumElements() > Src1NumElts) {
       Src1 = IC.Builder.CreateExtractVector(
-          FixedVectorType::get(Src0Ty->getElementType(), Src1NumElts), Src1,
+          FixedVectorType::get(Src1Ty->getElementType(), Src1NumElts), Src1,
           IC.Builder.getInt64(0));
       MadeChange = true;
     }