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>

package/mongodb/mongodb.mk

@@ -9,7 +9,7 @@ MONGODB_VERSION = r$(MONGODB_VERSION_BASE)
 MONGODB_SITE = $(call github,mongodb,mongo,$(MONGODB_VERSION))
 
 MONGODB_LICENSE = AGPLv3, Apache-2.0
-MONGODB_LICENSE_FILES = GNU-AGPL-3.0.txt, APACHE-2.0.txt
+MONGODB_LICENSE_FILES = GNU-AGPL-3.0.txt APACHE-2.0.txt
 
 MONGODB_DEPENDENCIES = host-scons