media: dvb_frontends: fix kernel-doc macros

Now, the Kernel checks for kernel_doc format issues.
Weird enough, it didn't get any of those troubles. Shssst!

Well, let's fix it, as a preventive way to avoid having
hundreds of new warnings on some next Linux version.

Tested by adding all files under dvb-frontends that have
"/**" on them.

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

drivers/media/dvb-frontends/helene.h

@@ -38,6 +38,7 @@ enum helene_xtal {
  * @set_tuner_priv:	Callback function private context
  * @set_tuner_callback:	Callback function that notifies the parent driver
  *			which tuner is active now
+ * @xtal: Cristal frequency as described by &enum helene_xtal
  */
 struct helene_config {
 	u8	i2c_address;