drivers/rapidio/rio_cm.c: fix potential oops in riocm_ch_listen()

If riocm_get_channel() fails, then we should just return -EINVAL.
Calling riocm_put_channel() will trigger a NULL dereference and
generally we should call put() if the get() didn't succeed.

Link: http://lkml.kernel.org/r/20190110130230.GB27017@kadam
Fixes: b6e8d4a ("rapidio: add RapidIO channelized messaging driver")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Matt Porter <mporter@kernel.crashing.org>
Cc: Alexandre Bounine <alexandre.bounine@idt.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/rapidio/rio_cm.c

@@ -1215,7 +1215,9 @@ static int riocm_ch_listen(u16 ch_id)
 	riocm_debug(CHOP, "(ch_%d)", ch_id);
 
 	ch = riocm_get_channel(ch_id);
-	if (!ch || !riocm_cmp_exch(ch, RIO_CM_CHAN_BOUND, RIO_CM_LISTEN))
+	if (!ch)
+		return -EINVAL;
+	if (!riocm_cmp_exch(ch, RIO_CM_CHAN_BOUND, RIO_CM_LISTEN))
 		ret = -EINVAL;
 	riocm_put_channel(ch);
 	return ret;