drm/panthor: Fix off by one in panthor_fw_get_cs_iface()

The ->iface.streams[csg_slot][] array has MAX_CS_PER_CSG elements so
this > comparison needs to be >= to prevent an out of bounds access.

Fixes: 2718d918 ("drm/panthor: Add the FW logical block")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/62835c16-c85c-483d-a8fe-63be78d49d15@moroto.mountain