fix configure -commercial

Commit 0aad3fc742a7aa15c21fe75e2b1b001f1f73468c broke
"configure -commercial". The license check needs to know where Qt's
source directory is.

Change-Id: I5e53135b6b628eb5e413b2c2b3b8721dae02b503
Reviewed-by: Sergio Ahumada <sergio.ahumada@digia.com>
Reviewed-by: Kalle Viironen <kalle.viironen@digia.com>
Reviewed-by: Iikka Eklund <iikka.eklund@digia.com>