qtiffhandler: correct types for height and width

qMin() was used with quint32 and uint32. This fixes the build on Haiku.

Change-Id: I193f561b9a63ffe9ee5ae991084118a821e3f22d
Reviewed-by: Augustin Cavalier <waddlesplash@gmail.com>
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@qt.io>