agx: Update RA comment

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16268>

src/asahi/compiler/agx_register_allocate.c

@@ -24,11 +24,7 @@
 #include "agx_compiler.h"
 #include "agx_builder.h"
 
-/* Trivial register allocator that never frees anything.
- *
- * TODO: Write a real register allocator.
- * TODO: Handle phi nodes.
- */
+/* SSA-based register allocator */
 
 /** Returns number of registers written by an instruction */
 unsigned