media: docs: make V4L 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/v4l/func-open.rst

@@ -1,4 +1,5 @@
 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
+.. c:namespace:: V4L
 
 .. _func-open:
 
@@ -11,7 +12,6 @@ Name
 
 v4l2-open - Open a V4L2 device
 
-
 Synopsis
 ========
 
@@ -19,9 +19,7 @@ Synopsis
 
     #include <fcntl.h>
 
-
 .. c:function:: int open( const char *device_name, int flags )
-    :name: v4l2-open
 
 Arguments
 =========
@@ -34,7 +32,7 @@ Arguments
     technicality, input devices still support only reading and output
     devices only writing.
 
-    When the ``O_NONBLOCK`` flag is given, the :ref:`read() <func-read>`
+    When the ``O_NONBLOCK`` flag is given, the :c:func:`read()`
     function and the :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl will
     return the ``EAGAIN`` error code when no data is available or no
     buffer is in the driver outgoing queue, otherwise these functions
@@ -43,22 +41,20 @@ Arguments
 
     Other flags have no effect.
 
-
 Description
 ===========
 
-To open a V4L2 device applications call :ref:`open() <func-open>` with the
+To open a V4L2 device applications call :c:func:`open()` with the
 desired device name. This function has no side effects; all data format
 parameters, current input or output, control values or other properties
-remain unchanged. At the first :ref:`open() <func-open>` call after loading the
+remain unchanged. At the first :c:func:`open()` call after loading the
 driver they will be reset to default values, drivers are never in an
 undefined state.
 
-
 Return Value
 ============
 
-On success :ref:`open() <func-open>` returns the new file descriptor. On error
+On success :c:func:`open()` returns the new file descriptor. On error
 -1 is returned, and the ``errno`` variable is set appropriately.
 Possible error codes are: