binman: Correct comment in blob_dtb GetFdtEtype()

The filenames are a bit confused. Fix them.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/binman/etype/blob_dtb.py b/tools/binman/etype/blob_dtb.py
index d543de9..1471ded 100644
--- a/tools/binman/etype/blob_dtb.py
+++ b/tools/binman/etype/blob_dtb.py
@@ -57,7 +57,9 @@
     def GetFdtEtype(self):
         """Get the entry type of this device tree
 
-        This can be 'u-boot-dtb', 'u-boot-spl-dtb' or 'u-boot-tpl-dtb'
+        This can be 'u-boot-dtb', 'u-boot-spl-dtb', 'u-boot-tpl-dtb' or
+        'u-boot-vpl-dtb'
+
         Returns:
             Entry type if any, e.g. 'u-boot-dtb'
         """