[SQL] fix typo in DataSourceRegister

## What changes were proposed in this pull request?
fix typo in DataSourceRegister

## How was this patch tested?

found when going through latest code

Author: Jacky Li <jacky.likun@huawei.com>

Closes #11686 from jackylk/patch-12.

sql/core/src/main/scala/org/apache/spark/sql/sources/interfaces.scala

@@ -57,7 +57,7 @@ trait DataSourceRegister {
    * overridden by children to provide a nice alias for the data source. For example:
    *
    * {{{
-   *   override def format(): String = "parquet"
+   *   override def shortName(): String = "parquet"
    * }}}
    *
    * @since 1.5.0