tcm_fc: Do not report target role when target is not defined

Clear the target role when no target is provided for
the node performing a PRLI.

Signed-off-by: Mark Rustad <mark.d.rustad@intel.com>
Reviewed-by: Bhanu Prakash Gollapudi <bprakash@broadcom.com>
Acked by Robert Love <robert.w.love@intel.com>
Cc: stable@vger.kernel.org
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>