drm/radeon: use variable flags as parameter

To be consistent with amdgpu driver, use "flags" as the parameter because
it is already assigned as "ent->driver_data".

Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Tested-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Wu Hoi Pok <wuhoipok@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>