modetest: only select plane with matching format

Don't assume that a plane supports any kind of pixelformat
but do a check first.

v2: Simplify the format check.
Signed-off-by: Tobias Jakobi <tjakobi@math.uni-bielefeld.de>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
1 file changed