[media] DocBook: better document FE_SET_TONE ioctl

Use the proper format for FE_SET_TONE documentation and
improve the documentation.

Keep the enum fe_sec_tone_mode description together with
the ioctl, as both are used together.

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

include/uapi/linux/dvb/frontend.h

@@ -114,10 +114,12 @@ enum fe_sec_voltage {
 typedef enum fe_sec_voltage fe_sec_voltage_t;
 
 
-typedef enum fe_sec_tone_mode {
+enum fe_sec_tone_mode {
 	SEC_TONE_ON,
 	SEC_TONE_OFF
-} fe_sec_tone_mode_t;
+};
+
+typedef enum fe_sec_tone_mode fe_sec_tone_mode_t;
 
 
 typedef enum fe_sec_mini_cmd {