ir3: fix freeing incorrect register in loops

While processing loop back edges, current live defs were freed through
their def pointer instead of correctly using get_def(). This may cause
the wrong register being freed when the current live def was reloaded.

Fixes: 21cd9b9557 ("ir3: implement RA for predicate registers")
Signed-off-by: Job Noorman <jnoorman@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/27986>

src/freedreno/ir3/ir3_ra_predicates.c

@@ -382,7 +382,7 @@ ra_block(struct ra_predicates_ctx *ctx, struct ir3_block *block)
 
          /* Different def in the same register, free it first. */
          if (cur_def->def)
-            free_reg(ctx, live, cur_def->def);
+            free_reg(ctx, live, get_def(cur_def));
 
          /* Reload the def in the required register right before the block's
           * terminator.