Spring Fix example in Javadoc for MultipartBodyBuilder

The example of MultipartBodyBuilder was wrong, so it was corrected.

Comment From: sbrannen

Hi @heoYH,

Good catch, and congratulations on submitting your first PR for the Spring Framework! 👍

Although .body(BodyInserters.fromMultipartData(multipartBody)) would work, I assume the intention was to use .bodyValue(multipartBody) instead.

So I'll merge this PR to give you credit and then change the example to use the more succinct bodyValue() method.

Comment From: sbrannen

This has been merged into 6.0.x and main.

Thanks