[AMDGPU] Fix comment for llvm.amdgcn.div.scale. NFC.

Update comment to reflect actual lowering.

Author: kerbowa

llvm/include/llvm/IR/IntrinsicsAMDGPU.td

@@ -217,8 +217,8 @@ def int_amdgcn_s_waitcnt : GCCBuiltin<"__builtin_amdgcn_s_waitcnt">,
 def int_amdgcn_div_scale : Intrinsic<
   // 1st parameter: Numerator
   // 2nd parameter: Denominator
-  // 3rd parameter: Constant to select between first and
-  //                second. (0 = first, 1 = second).
+  // 3rd parameter: Select quotient. Must equal Numerator or Denominator.
+  //                (0 = Denominator, 1 = Numerator).
   [llvm_anyfloat_ty, llvm_i1_ty],
   [LLVMMatchType<0>, LLVMMatchType<0>, llvm_i1_ty],
   [IntrNoMem, IntrSpeculatable, ImmArg<2>]