pan/bi: Consider all dests in helper_block_update

pan/bi: Consider all dests in helper_block_update

If an instruction has multiple destinations and *any* of them are needed by
helper invocations, we should keep helper invocations alive. This is a bug fix.
Consider the GLSL:

   first = texture(sampler, ...);
   float res = texture(sampler, vec2(first.y)).x + first.x;

Corresponding to the IR:

   first = ...
   x, y, z, w = SPLIT first
   second = TEX y, y
   x', y', z', w' = SPLIT second
   FADD res, x, x'

Here, x is not required by helper invocations (the coordinates to TEX) while y
is required. If we only look at only the first destinations, we incorrectly
decide that first is not required and fail to set the .skip bit, leading to
incorrect results.

Fixes: 5febeae58e0 ("pan/bi: Emit collect and split")
Signed-off-by: Alyssa Rosenzweig <alyssa@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17794>