tree: Make internal functions static

None of these functions are used outside of the files they are defined
in, so make them all static.

Change-Id: Ie9cbe12d289bcedacf2f1bf483ae64ef8039ccc1
Signed-off-by: Jacob Garber <jgarber1@ualberta.ca>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/33667
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: HAOUAS Elyes <ehaouas@noos.fr>
Reviewed-by: Nico Huber <nico.h@gmx.de>
diff --git a/hwaccess.c b/hwaccess.c
index acb99f8..bb5aac4 100644
--- a/hwaccess.c
+++ b/hwaccess.c
@@ -223,7 +223,7 @@
 	};
 };
 
-int undo_mmio_write(void *p)
+static int undo_mmio_write(void *p)
 {
 	struct undo_mmio_write_data *data = p;
 	msg_pdbg("Restoring MMIO space at %p\n", data->addr);