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/gfxnvidia.c b/gfxnvidia.c
index c6d752e..d8ea4d6 100644
--- a/gfxnvidia.c
+++ b/gfxnvidia.c
@@ -28,7 +28,7 @@
 #define GFXNVIDIA_MEMMAP_MASK		((1 << 17) - 1)
 #define GFXNVIDIA_MEMMAP_SIZE		(16 * 1024 * 1024)
 
-uint8_t *nvidia_bar;
+static uint8_t *nvidia_bar;
 
 const struct dev_entry gfx_nvidia[] = {
 	{0x10de, 0x0010, NT, "NVIDIA", "Mutara V08 [NV2]" },