drm/i915/selftests: remove a condition

We know that "err" is non-zero so there is no need to check.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20191213105050.y2v5nylsuxvc44jj@kili.mountain