accel/amdxdna: Remove __counted_by from struct amdxdna_cmd_chain

In the Linux kernel, the following vulnerability has been resolved: accel/amdxdna: Remove __counted_by from struct amdxdna_cmd_chain struct amdxdna_cmd_chain contains a flexible array annotated with __counted_by(command_count). Since the structure is stored in shared AMDXDNA_BO_SHARE memory, userspace can modify command_count concurrently. If command_count is changed to zero, the bounds check generated from __counted_by may fail and trigger a kernel panic. Remove __counted_by to avoid relying on the userspace-controlled command_count for the flexible array bounds check.