panfrost: fix typo in register allocation

The intention of the code was to allow PHI values to be propagated
if they were in registers (as opposed to in memory). As written though
values were never propagated. I think this typo was due to some
debug code that wasn't removed properly.

Fixes: 6c64ad934f ("panfrost: spill registers in SSA form")
Reviewed-by: Mary Guillemard <mary.guillemard@collabora.com>
Reviewed-by: Ashley Smith <ashley.smith@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/37092>

src/panfrost/compiler/bi_ra.c

@@ -965,7 +965,7 @@ bi_out_of_ssa(bi_context *ctx)
          }
 
          /* Replace the phi with a move */
-         allow_propagate = false;
+         allow_propagate = true;
          bi_builder b = bi_init_builder(ctx, bi_before_instr(I));
          if (I->dest[0].memory) {
             /* dest was spilled to memory */