[FLINK-11119][docs] Correct Scala example for Table Function in User-…

[wenhuitang]

What is the purpose of the change

This pull request corrects Scala example for Table Function in User-defined Functions docs.

Brief change log

Add "LATERAL" to sqlQuery string in Scala example for Table Function in User-defined Functions docs.
Correct Split#eval in Scala example for Table Function in User-defined Functions docs.

Verifying this change

This change is a trivial rework / code cleanup without any test coverage.

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): no
• The public API, i.e., is any changed class annotated with @Public(Evolving): (yes / no)
• The serializers: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Yarn/Mesos, ZooKeeper: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? no
• If yes, how is the feature documented? not documented

[twalthr]

Thank you @wenhuitang. Merging...