[BUGFIX] Missing separator in tables.sql

[BUGFIX] Missing separator in tables.sql

For the table sys_category_record_mm after the first KEY command there is
a missing comma which leads to dbal crash.

Change-Id: Ib5d88df46c166a9e7fffd5106e5158679cd947d8
Fixes: #43167
Release: 6.0
Reviewed-on: http://review.typo3.org/16628
Reviewed-by: Anja Leichsenring
Reviewed-by: Philipp Gampe
Reviewed-by: Wouter Wolters
Reviewed-by: Helmut Hummel
Tested-by: Helmut Hummel