scons,misc: Fix broken X86_MI_example build_opts

This bug was causing the compiler tests to fail:
https://jenkins.gem5.org/job/compiler-checks/65/

Change-Id: I472a50a4a415108d177255fa396e67385104b059
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/53684
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
Reviewed-by: Gabe Black <gabe.black@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
diff --git a/build_opts/X86_MI_example b/build_opts/X86_MI_example
index 5fb47a3..60d1645 100644
--- a/build_opts/X86_MI_example
+++ b/build_opts/X86_MI_example
@@ -1,3 +1,3 @@
 TARGET_ISA = 'x86'
 CPU_MODELS = 'TimingSimpleCPU,O3CPU,AtomicSimpleCPU'
-PROTOCOL = 'MI_example
+PROTOCOL = 'MI_example'