arch-x86: Fix a bug in the protected mode IRET.

Fix the direction of the comparison which makes sure the new RIP will
fit within the new CS limit.

Change-Id: I3f3e66c185d0e1fbc430b0ae594d63cdd62b9dfd
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/55887
Reviewed-by: Matt Sinclair <mattdsinclair@gmail.com>
Maintainer: Gabe Black <gabe.black@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/arch/x86/isa/insts/general_purpose/control_transfer/interrupts_and_exceptions.py

@@ -156,7 +156,7 @@ processCSDescriptor:
     # appropriate/other RIP checks.
     # if temp_RIP > CS.limit throw #GP(0)
     rdlimit t6, cs, dataSize=8
-    sub t0, t1, t6, flags=(ECF,)
+    sub t0, t6, t1, flags=(ECF,)
     fault "std::make_shared<GeneralProtection>(0)", flags=(CECF,)
 
     #(temp_CPL!=CPL)