Add missing NULL point check inside ixgbe_pf_host_uninit, or it may cause
segment fault when detaching a device.
Fixes: cf80ba6e2038 ("net/ixgbe: add support for representor ports")
Cc: stable@dpdk.org
Signed-off-by: Qi Zhang <qi.z.zhang@intel.com>
Acked-by: Remy Horton <remy.horton@intel.com>