etnaviv: fix shader miscompilation with more than 16 labels

etnaviv: fix shader miscompilation with more than 16 labels

The labels array may change its virtual address on a reallocation, so
it is invalid to cache pointers into the array. Rather than using the
pointer directly, remember the array index.

Fixes miscompilation of shaders in glmark2 ideas, leading to GPU hangs.

Fixes: c9e8b49b (etnaviv: gallium driver for Vivante GPUs)
Cc: mesa-stable@lists.freedesktop.org
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>