📝 docs(smolvlm): fix variable name in batch inference example (#42123)

Fixed incorrect variable name on line 162. The code creates a list called
'conversations' (plural) but incorrectly references 'conversation' (singular)
in the apply_chat_template call, which would cause a NameError.

This fixes the batch mixed media inference example to use the correct
variable name, allowing the code to run without errors.

Author: gorkachea

docs/source/en/model_doc/smolvlm.md

@@ -159,7 +159,7 @@ conversation3 = [
 
 conversations = [conversation1, conversation2, conversation3]
 inputs = processor.apply_chat_template(
-    conversation,
+    conversations,
     add_generation_prompt=True,
     tokenize=True,
     return_dict=True,