ffmpeg: fix camera selection on linux


Merging aeadc3b96 re-established the eager v4l2 camera selection on
linux. This was bypassing the camera backend selection from
selectedCameraBackend.

Change-Id: I927b78cdd3320cd8962daccd10e3956628ddeccd
Reviewed-by: Mikko Hallamaa <mikko.hallamaa@qt.io>
commitd9f5abf2d3f86a27abd7ecdc2a66cc3e3353d6ed
parentddbfa91ceedfa3d990e9aa9b870618a7b069ae60
authorTim Blechmann <tim.blechmann@qt.io>
committerTim Blechmann <tim.blechmann@qt.io>
commit timeWed, 21 Oct 2026 06:26:06 +0000