stage_cache: make prog const in stage_cache_add()

The stage_cache_add() function should not be manipulating
the struct prog argument in anyway. Therefore, mark it as
const.

BUG=chrome-os-partner:43636
BRANCH=None
TEST=Built, booted, suspended, and resumed on glados.

Original-Change-Id: I4509e478d3c98247b9d776f6534b949d9ba6282c
Original-Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/290721
Original-Reviewed-by: Leroy P Leahy <leroy.p.leahy@intel.com>
Original-Reviewed-by: Duncan Laurie <dlaurie@chromium.org>

Change-Id: Ibadc00a9e1cbbf12119def92d77a79077625fb85
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/11192
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
diff --git a/src/include/stage_cache.h b/src/include/stage_cache.h
index 5a4c16a..68cfdb7 100644
--- a/src/include/stage_cache.h
+++ b/src/include/stage_cache.h
@@ -30,7 +30,7 @@
 };
 
 /* Cache the loaded stage provided according to the parameters. */
-void stage_cache_add(int stage_id, struct prog *stage);
+void stage_cache_add(int stage_id, const struct prog *stage);
 /* Load the cached stage at given location returning the stage entry point. */
 void stage_cache_load_stage(int stage_id, struct prog *stage);
 /* Fill in parameters for the external stage cache, if utilized. */