vfio: fix FreeBSD clear group stub
vfio: fix FreeBSD clear group stub

On FreeBSD, `rte_vfio_clear_group()` was returning 0 even though this
function is not valid for FreeBSD, and is called out to return error in
doxygen comments.
Fix the return value to match documentation.

Fixes: c564a2a20093 ("vfio: expose clear group function for internal usages")
Cc: stable@dpdk.org

Signed-off-by: Anatoly Burakov <814e00d8f6e4e81b7ccc7e3e5a0bfec0078f0203@intel.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk