V4L/DVB: saa7164: move dereference under NULL check

The original code dereferenced "port" before checking it for NULL.  I
moved the test down below the check.  Also I changed the comparisons a
little so people wouldn't get confused and think "port" and "buf" were
ints instead of pointers.  (Probably that's what lead to this issue in
the first place.)

There is only one caller for this function and it passes non-NULL
pointers, so this is essentially a cleanup rather than a bugfix.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/saa7164/saa7164-buffer.c

@@ -136,10 +136,11 @@ ret:
 int saa7164_buffer_dealloc(struct saa7164_tsport *port,
 	struct saa7164_buffer *buf)
 {
-	struct saa7164_dev *dev = port->dev;
+	struct saa7164_dev *dev;
 
-	if ((buf == 0) || (port == 0))
+	if (!buf || !port)
 		return SAA_ERR_BAD_PARAMETER;
+	dev = port->dev;
 
 	dprintk(DBGLVL_BUF, "%s() deallocating buffer @ 0x%p\n", __func__, buf);