target: Cleanup transport_kunmap_data_sg()

This code isn't broken per se, but it's scary to look at! It looks like
in the t_data_nents==1 case we're doing both a kunmap and a vunmap,
what's saving us is that t_data_vmap in this case is 0, so vunmap
doesn't do anything.

Return after kunmap, so the handling of the three cases does not overlap.
Signed-off-by: Andy Grover <agrover@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/target_core_transport.c

@@ -3546,10 +3546,12 @@ EXPORT_SYMBOL(transport_kmap_data_sg);
 
 void transport_kunmap_data_sg(struct se_cmd *cmd)
 {
-	if (!cmd->t_data_nents)
+	if (!cmd->t_data_nents) {
 		return;
-	else if (cmd->t_data_nents == 1)
+	} else if (cmd->t_data_nents == 1) {
 		kunmap(sg_page(cmd->t_data_sg));
+		return;
+	}
 
 	vunmap(cmd->t_data_vmap);
 	cmd->t_data_vmap = NULL;