address review comments

Author: Thorsten Schütt

llvm/test/CodeGen/AArch64/GlobalISel/combine-cast.mir

@@ -233,3 +233,4 @@ body:             |
     %large:_(<2 x s64>) = G_ZEXT %undef(<2 x s32>)
     $q0 = COPY %large(<2 x s64>)
     $d0 = COPY %undef(<2 x s32>)
+...