drm: Fix error handling in drm_mm eviction kselftest

        drivers/gpu/drm/selftests/test-drm_mm.c:1277 evict_everything()
        warn: calling list_del() inside list_for_each

The list_del() inside the error handling in the eviction loop is
overkill. We have to undo the eviction scan to return the drm_mm back to
a recoverable state, so have to iterate over the full list, but we only
want to report the error once and once we have an error we can return
early.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Fixes: 560b3284 ("drm: kselftest for drm_mm and eviction")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20170110144031.7609-1-chris@chris-wilson.co.uk