KVM: fix emulator_task_switch() return value.

emulator_task_switch() should return -1 for failure and 0 for success to
the caller, just like x86_emulate_insn() does.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 585d0ef..5ac0bb4 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -2453,7 +2453,7 @@
 		rc = writeback(ctxt, ops);
 	}
 
-	return rc;
+	return (rc == X86EMUL_UNHANDLEABLE) ? -1 : 0;
 }
 
 static void string_addr_inc(struct x86_emulate_ctxt *ctxt, unsigned long base,