binman: fix default filename of u-boot-with-ucode-ptr in documentation

The suffix should be ".bin" instead of ".dtb" .

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/binman/README.entries b/tools/binman/README.entries
index 0576e63..6a816bb 100644
--- a/tools/binman/README.entries
+++ b/tools/binman/README.entries
@@ -971,7 +971,7 @@
 --------------------------------------------------------------------
 
 Properties / Entry arguments:
-    - filename: Filename of u-boot-nodtb.dtb (default 'u-boot-nodtb.dtb')
+    - filename: Filename of u-boot-nodtb.bin (default 'u-boot-nodtb.bin')
     - optional-ucode: boolean property to make microcode optional. If the
         u-boot.bin image does not include microcode, no error will
         be generated.