radv: pass the ACQUIRE_MEM engine enum, not the WRITE_DATA one

radv_create_flush_postamble() hands ac_emit_cp_acquire_mem() the constant
V_581A_PREFETCH_PARSER, but that belongs to a different packet's engine
field.  ac_emit_cp_acquire_mem() wants the ACQUIRE_MEM engine selector and
says so:

  assert(ip_type != AMD_IP_GFX || (engine == V_581B_CP_PFP || engine == V_581B_CP_ME));

so an assertions-enabled build aborts:

  vkcube: ../src/amd/common/ac_cmdbuf_cp.c:406: ac_emit_cp_acquire_mem:
  Assertion `ip_type != AMD_IP_GFX || (engine == V_581B_CP_PFP ||
  engine == V_581B_CP_ME)' failed.

V_581A_PREFETCH_PARSER and V_581B_CP_PFP name the same thing - the prefetch
parser - they are just the enums of two different packets, so use the one
this function is documented to take.  Every other caller in radv_cs.c
already passes V_581B_CP_PFP.

This is only reachable on GFX6/GFX7:

  if (pdev->info.gfx_level <= GFX7 &&
      (queue->state.qf == RADV_QUEUE_GENERAL || queue->state.qf == RADV_QUEUE_COMPUTE))
	  result = radv_create_flush_postamble(queue);

and on those chips ac_emit_cp_acquire_mem() takes the pre-GFX9 branch, which
emits PKT3_SURFACE_SYNC and never looks at the engine argument at all.  So
no packet changes on this hardware - only the bogus assertion goes away.
From GFX10 on the argument does select the engine, and there the value would
have been wrong, but no chip that new reaches this code.

Found on an HP rx2660 (ia64) with an Oland; nothing here is ia64 specific,
it just needs old hardware and a Mesa built with assertions.

Signed-off-by: René Rebe <rene@exactco.de>

--- mesa-26.1.6/src/amd/vulkan/radv_queue.c
+++ mesa-26.1.6/src/amd/vulkan/radv_queue.c
@@ -1369,7 +1369,7 @@ radv_create_flush_postamble(struct radv_
          S_0085F0_DB_ACTION_ENA(1) |
          S_0085F0_DB_DEST_BASE_ENA(1);
 
-   ac_emit_cp_acquire_mem(cs->b, pdev->info.gfx_level, cs->hw_ip, V_581A_PREFETCH_PARSER, cp_coher_cntl);
+   ac_emit_cp_acquire_mem(cs->b, pdev->info.gfx_level, cs->hw_ip, V_581B_CP_PFP, cp_coher_cntl);
 
    result = radv_finalize_cmd_stream(device, cs);
    if (result != VK_SUCCESS) {