mksrc: Rename 'commercial' with 'enterprise'

This will create a qt-everywhere-enterprise-src-<VERSION> source
packages instead.

Change-Id: I78bcbe73c9b7f1bdac3b757c2bfc802870efc669
Reviewed-by: Andy Shaw <andy.shaw@digia.com>
Reviewed-by: Iikka Eklund <iikka.eklund@digia.com>