media: docs: make DVB documents more compatible with Sphinx 3.1+

Sphinx 3.x broke support for the cdomain.py extension, as the
c domain code was rewritten. Due to that, the c tags need to
be re-written, in order to use the new c domain notation.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

Documentation/userspace-api/media/dvb/fe-set-frontend.rst

@@ -1,4 +1,5 @@
 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
+.. c:namespace:: DTV.fe
 
 .. _FE_SET_FRONTEND:
 
@@ -13,24 +14,22 @@ Name
 
 FE_SET_FRONTEND
 
-
 Synopsis
 ========
 
-.. c:function:: int ioctl(int fd, FE_SET_FRONTEND, struct dvb_frontend_parameters *p)
-    :name: FE_SET_FRONTEND
+.. c:macro:: FE_SET_FRONTEND
 
+``int ioctl(int fd, FE_SET_FRONTEND, struct dvb_frontend_parameters *p)``
 
 Arguments
 =========
 
 ``fd``
-    File descriptor returned by :c:func:`open() <dvb-fe-open>`.
+    File descriptor returned by :c:func:`open()`.
 
 ``p``
     Points to parameters for tuning operation.
 
-
 Description
 ===========
 
@@ -44,7 +43,6 @@ operation is initiated before the previous one was completed, the
 previous operation will be aborted in favor of the new one. This command
 requires read/write access to the device.
 
-
 Return Value
 ============
 
@@ -66,6 +64,5 @@ appropriately.
 
        -  Maximum supported symbol rate reached.
 
-
 Generic error codes are described at the
 :ref:`Generic Error Codes <gen-errors>` chapter.