Prevent crash if random DTB address is passed to bootm

This patch adds bootm_start() return value check. If
error status is returned, we do not proceed further to
prevent board reset or crash as we still can recover
at this point.

Signed-off-by: Anatolij Gustschin <agust@denx.de>

common/image.c

@@ -1516,7 +1516,7 @@ int boot_get_fdt (int flag, int argc, char *argv[], bootm_headers_t *images,
 			}
 			break;
 		default:
-			fdt_error ("Did not find a cmdline Flattened Device Tree");
+			puts ("ERROR: Did not find a cmdline Flattened Device Tree\n");
 			goto error;
 		}