target:fix condition return in core_pr_dump_initiator_port()

When is pr_reg->isid_present_at_reg is false,this function should return.

This fixes a regression originally introduced by:

  commit d2843c17
  Author: Andy Grover <agrover@redhat.com>
  Date:   Thu May 16 10:40:55 2013 -0700

      target: Alter core_pr_dump_initiator_port for ease of use
Signed-off-by: tangwenji <tang.wenji@zte.com.cn>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/target_core_pr.c

@@ -58,8 +58,10 @@ void core_pr_dump_initiator_port(
 	char *buf,
 	u32 size)
 {
-	if (!pr_reg->isid_present_at_reg)
+	if (!pr_reg->isid_present_at_reg) {
 		buf[0] = '\0';
+		return;
+	}
 
 	snprintf(buf, size, ",i,0x%s", pr_reg->pr_reg_isid);
 }