[SQL][MINOR] Fix scaladoc for UDFRegistration

## What changes were proposed in this pull request?

Fix scaladoc for UDFRegistration

## How was this patch tested?

local build

Author: Jacek Laskowski <jacek@japila.pl>

Closes #17337 from jaceklaskowski/udfregistration-scaladoc.

(cherry picked from commit 6326d406)
Signed-off-by: Reynold Xin <rxin@databricks.com>