image: Rename load_addr, save_addr, save_size

These global variables are quite short and generic. In fact the same name
is more often used locally for struct members and function arguments.

Add a image_ prefix to make them easier to distinguish.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/cmd/elf.c b/cmd/elf.c
index 32f12a7..57736f9 100644
--- a/cmd/elf.c
+++ b/cmd/elf.c
@@ -294,7 +294,7 @@
 		/* Consume address */
 		argc--; argv++;
 	} else
-		addr = load_addr;
+		addr = image_load_addr;
 
 	if (!valid_elf_image(addr))
 		return 1;
@@ -348,7 +348,7 @@
 	 * If we don't know where the image is then we're done.
 	 */
 	if (argc < 2)
-		addr = load_addr;
+		addr = image_load_addr;
 	else
 		addr = simple_strtoul(argv[1], NULL, 16);