Add @simonmar to various things in CODEOWNERS

CODEOWNERS

@@ -21,9 +21,10 @@
 /compiler/typecheck/TcDeriv*     @RyanGlScott
 /compiler/nativeGen              @simonmar @bgamari @AndreasK
 /compiler/llvmGen                @angerman
-/compiler/codeGen                @osa1
-/compiler/cmm                    @osa1
-/compiler/simplCore/CallArity.hs @nomeata @sgraf
+/compiler/codeGen                @simonmar @osa1
+/compiler/cmm                    @simonmar @osa1
+/compiler/ghci                   @simonmar
+/compiler/simplCore/CallArity.hs @nomeata
 /compiler/utils/UnVarGraph.hs    @nomeata
 /compiler/simplCore/Exitify.hs   @nomeata
 /compiler/simplStg/StgCse.hs     @nomeata