tree: Make internal variables static

All these variables are only used in the files they are defined in, so
they can be made static.

Change-Id: I1e55138adef540e9d3a2237aa5b289cb338c0608
Signed-off-by: Jacob Garber <jgarber1@ualberta.ca>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/33747
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>
diff --git a/layout.c b/layout.c
index e49189e..6e476c2 100644
--- a/layout.c
+++ b/layout.c
@@ -24,7 +24,7 @@
 #include "programmer.h"
 #include "layout.h"
 
-struct romentry entries[MAX_ROMLAYOUT];
+static struct romentry entries[MAX_ROMLAYOUT];
 static struct flashrom_layout global_layout = { entries, 0 };
 
 struct flashrom_layout *get_global_layout(void)