mongodb: fix legal info build error

Remove extra comma to fix legal info build error.

Fixes:
http://autobuild.buildroot.net/results/87faca89bc9ff6ff4699c4b50bbb890ff80b95ee/
http://autobuild.buildroot.net/results/ea54721ef0d1c210b2baa9eef7c6c68863020b50/
http://autobuild.buildroot.net/results/5a81db472d432880f44dfb30bae0d777b6ae6c79/


...

Signed-off-by: Sergio Prado <sergio.prado@e-labworks.com>
Acked-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>