bus/fslmc: fix VFIO group descriptor check

bus/fslmc: fix VFIO group descriptor check

The issue is that a file descriptor at 0 is a valid one. Currently
the file not found, the return value will be set to 0. As a result,
it is impossible to distinguish between a correct descriptor and a
failed return value. Fix it to return -ENOENT instead of 0.

Fixes: a69f79300262 ("bus/fslmc: support multi VFIO group")
Cc: stable@dpdk.org
Signed-off-by: Yunjian Wang <wangyunjian@huawei.com>
Acked-by: Anatoly Burakov <anatoly.burakov@intel.com>
Acked-by: Hemant Agrawal <hemant.agrawal@nxp.com>