pktcdvd: fix error return code

Set the return variable to an error code as done elsewhere in the function.

A simplified version of the semantic match that finds this problem is as
follows: (http://coccinelle.lip6.fr/)

// <smpl>
(
if@p1 (\(ret < 0\|ret != 0\))
 { ... return ret; }
|
ret@p1 = 0
)
... when != ret = e1
    when != &ret
*if(...)
{
  ... when != ret = e2
      when forall
 return ret;
}

// </smpl>
Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/block/pktcdvd.c

@@ -706,7 +706,9 @@ static int pkt_generic_packet(struct pktcdvd_device *pd, struct packet_command *
 			     WRITE : READ, __GFP_WAIT);
 
 	if (cgc->buflen) {
-		if (blk_rq_map_kern(q, rq, cgc->buffer, cgc->buflen, __GFP_WAIT))
+		ret = blk_rq_map_kern(q, rq, cgc->buffer, cgc->buflen,
+				      __GFP_WAIT);
+		if (ret)
 			goto out;
 	}