backends/drm: fix format choosing

Xaver Hugl requested to merge work/Plasma-5-24-format into Plasma/5.24

The logic was inverted and would choose the format after the first one that is suitable. On most hardware that wouldn't cause noticable issues as that will choose the ARGB variant of the normal format, but some Intel hardware doesn't support these and thus a lower bit depth format than intended gets used.

This is 5.24-only, !2044 (merged) already fixes this better for master

BUG: 450779

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