Add missing virtual destructor for new class

qmediaserviceproviderplugin.h:166:28: error: ‘struct QMediaServiceCameraInfoInterface’ has virtual functions and accessible non-virtual destructor [-Werror=non-virtual-dtor]

Change-Id: I08c6718bfd87c5adeea9969afdd4766150163238
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@digia.com>
Reviewed-by: Yoann Lopes <yoann.lopes@digia.com>