[SQL] Fixed 2 comment typos in SQLConf

Author: Cheng Lian <lian.cs.zju@gmail.com>

Closes #2172 from liancheng/sqlconf-typo and squashes the following commits:

115cc71 [Cheng Lian] Fixed 2 comment typos in SQLConf

(cherry picked from commit 68f75dcdfe7e8ab229b73824692c4b3d4c39946c)
Signed-off-by: Michael Armbrust <michael@databricks.com>