binman: Correct the comment for ATF entry type

This is wrongly referring to Intel ME, which should be ATF.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/binman/etype/atf_bl31.py b/tools/binman/etype/atf_bl31.py
index 163d714..2041da4 100644
--- a/tools/binman/etype/atf_bl31.py
+++ b/tools/binman/etype/atf_bl31.py
@@ -2,7 +2,7 @@
 # Copyright 2020 Google LLC
 # Written by Simon Glass <sjg@chromium.org>
 #
-# Entry-type module for Intel Management Engine binary blob
+# Entry-type module for ARM Trusted Firmware binary blob
 #
 
 from binman.etype.blob_named_by_arg import Entry_blob_named_by_arg