freedreno/ir3: Link directly to Sethi-Ullman paper

Allow a direct link to the PDF itself from the authors themselves,
rather than a paywall splash page.

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Acked-by: Rob Clark <robdclark@chromium.org>

src/freedreno/ir3/ir3_sun.c

@@ -38,7 +38,7 @@
  * is computed in multiple paths into a block, I think we should only have to
  * consider the worst-case.
  *
- * [1] https://pdfs.semanticscholar.org/ae53/6010b214612c2571f483354c264b0b39c545.pdf
+ * [1] https://www.cs.princeton.edu/~appel/papers/sun.pdf
  */
 
 static unsigned