[SPDK] why discarding error output in setup.sh

Hi,

We have a question in spdk/scripts/setup.sh. In this commit
<https://github.com/spdk/spdk/commit/21173cd036e1af988463ea7a678347a27b555cb7#diff-1d889b31bb06cb578abde8e2253d043aR34>.
We can find that "2>/dev/null" was added:
echo "$bdf" > "/sys/bus/pci/drivers/$driver_name/bind" 2> /dev/null || true

May I know any specific reason for this? We tried to remove "2>/dev/null",
and indeed found error output:

> echo: write error: No such device
>
But the function of the script was still OK.

Thanks,
-Crane