bootm: allow correct bounds-check of destination

While nothing presently examines the destination size, it should at
least be correct so that future users of sys_mapmem() will not be
surprised. Without this, it might be possible to overflow memory.
Signed-off-by: NKees Cook <keescook@chromium.org>
Acked-by: NSimon Glass <sjg@chromium.org>

common/cmd_bootm.c

@@ -368,7 +368,7 @@ static int bootm_load_os(bootm_headers_t *images, unsigned long *load_end,
 
 	const char *type_name = genimg_get_type_name(os.type);
 
-	load_buf = map_sysmem(load, image_len);
+	load_buf = map_sysmem(load, unc_len);
 	image_buf = map_sysmem(image_start, image_len);
 	switch (comp) {
 	case IH_COMP_NONE: