AMDGPU: Fix a comment (#169403)

This verifier check will complain if there aren't enough implicit
operands -- so it doesn't *allow* those operands, it *requires* them.

Author: nhaehnle

llvm/lib/Target/AMDGPU/SIInstrInfo.cpp

@@ -5518,9 +5518,10 @@ bool SIInstrInfo::verifyInstruction(const MachineInstr &MI,
         Desc.getNumOperands() + Desc.implicit_uses().size();
     const unsigned NumImplicitOps = IsDst ? 2 : 1;
 
-    // Allow additional implicit operands. This allows a fixup done by the post
-    // RA scheduler where the main implicit operand is killed and implicit-defs
-    // are added for sub-registers that remain live after this instruction.
+    // Require additional implicit operands. This allows a fixup done by the
+    // post RA scheduler where the main implicit operand is killed and
+    // implicit-defs are added for sub-registers that remain live after this
+    // instruction.
     if (MI.getNumOperands() < StaticNumOps + NumImplicitOps) {
       ErrInfo = "missing implicit register operands";
       return false;