media: dmxdev: Fix the logic that enables DMA mmap support

Some conditions required for DVB mmap support to work are reversed.
Also, the logic is not too clear.

So, improve the logic, making it easier to be handled.

PS.: I'm pretty sure that I fixed it while testing, but, somehow,
the change got lost.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

include/media/dmxdev.h

@@ -163,6 +163,7 @@ struct dmxdev_filter {
  * @demux:		pointer to &struct dmx_demux.
  * @filternum:		number of filters.
  * @capabilities:	demux capabilities as defined by &enum dmx_demux_caps.
+ * @may_do_mmap:	flag used to indicate if the device may do mmap.
  * @exit:		flag to indicate that the demux is being released.
  * @dvr_orig_fe:	pointer to &struct dmx_frontend.
  * @dvr_buffer:		embedded &struct dvb_ringbuffer for DVB output.
@@ -180,6 +181,7 @@ struct dmxdev {
 	int filternum;
 	int capabilities;
 
+	unsigned int may_do_mmap:1;
 	unsigned int exit:1;
 #define DMXDEV_CAP_DUPLEX 1
 	struct dmx_frontend *dvr_orig_fe;