graphics/digikam: fix build against current KDE Gear components

In the recent update [1] of KDE Gear a header file in net/akonadi-contacts
was moved from Akonadi/Contact/ContactSearchJob to
AkonadiContact/Akonadi/ContactSearchJob.

[1] e250aeb4a1399664907d0df0605a3577ba671609

Reported by: fluffy