media: ddbridge: check pointers before dereferencing

Fixes two warnings reported by smatch:

  drivers/media/pci/ddbridge/ddbridge-core.c:240 ddb_redirect() warn: variable dereferenced before check 'idev' (see line 238)
  drivers/media/pci/ddbridge/ddbridge-core.c:240 ddb_redirect() warn: variable dereferenced before check 'pdev' (see line 238)

Fixed by moving the existing checks up before accessing members.

Cc: Ralph Metzler <rjkm@metzlerbros.de>
Signed-off-by: Daniel Scheller <d.scheller@gmx.net>
Tested-by: Richard Scobie <r.scobie@clear.net.nz>
Tested-by: Jasmin Jessich <jasmin@anw.at>
Tested-by: Dietmar Spingler <d_spingler@freenet.de>
Tested-by: Manfred Knick <Manfred.Knick@t-online.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

drivers/media/pci/ddbridge/ddbridge-core.c

@@ -170,10 +170,10 @@ static int ddb_redirect(u32 i, u32 p)
 	struct ddb *pdev = ddbs[(p >> 4) & 0x3f];
 	struct ddb_port *port;
 
-	if (!idev->has_dma || !pdev->has_dma)
-		return -EINVAL;
 	if (!idev || !pdev)
 		return -EINVAL;
+	if (!idev->has_dma || !pdev->has_dma)
+		return -EINVAL;
 
 	port = &pdev->port[p & 0x0f];
 	if (!port->output)