scipts: imgtool: bugfix #2096

fixing broken encryption caused by shift in function parameters.

Signed-off-by: Mateusz Michalek <mateusz.michalek@nordicsemi.no>
diff --git a/scripts/imgtool/main.py b/scripts/imgtool/main.py
index 94952a8..009d923 100755
--- a/scripts/imgtool/main.py
+++ b/scripts/imgtool/main.py
@@ -510,7 +510,7 @@
         }
 
     img.create(key, public_key_format, enckey, dependencies, boot_record,
-               custom_tlvs, compression_tlvs, int(encrypt_keylen), clear,
+               custom_tlvs, compression_tlvs, None, int(encrypt_keylen), clear,
                baked_signature, pub_key, vector_to_sign, user_sha)
 
     if compression in ["lzma2", "lzma2armthumb"]: