igt/drm_read: Clear O_NONBLOCK between tests
igt/drm_read: Clear O_NONBLOCK between tests

Ensure that O_NONBLOCK isn't accidentally set when we want a nonblocking
file descroptor.

Signed-off-by: Chris Wilson <711c73f64afdce07b7e38039a96d2224209e9a6c@chris-wilson.co.uk>

tiagovignatti/intel-gpu-tools,tiagovignatti/intel-gpu-tools,tiagovignatti/intel-gpu-tools,tiagovignatti/intel-gpu-tools