staging: bcm2835-codec: Fix potentially uninitialised vars

src_m2m_buf and dst_m2m_buf were printed in log messages
when there are code paths that don't initialise them.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.org>

drivers/staging/vc04_services/bcm2835-codec/bcm2835-v4l2-codec.c

@@ -743,7 +743,7 @@ static void device_run(void *priv)
 	struct bcm2835_codec_ctx *ctx = priv;
 	struct bcm2835_codec_dev *dev = ctx->dev;
 	struct vb2_v4l2_buffer *src_buf, *dst_buf;
-	struct m2m_mmal_buffer *src_m2m_buf, *dst_m2m_buf;
+	struct m2m_mmal_buffer *src_m2m_buf = NULL, *dst_m2m_buf = NULL;
 	struct v4l2_m2m_buffer *m2m;
 	int ret;