[media] DocBook: in non-blocking mode return EAGAIN in hwseek

VIDIOC_S_HW_FREQ_SEEK should return EAGAIN when called in non-blocking
mode. This might change in the future if we add support for this in the
future, but right now this is not supported.
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

Documentation/DocBook/media/v4l/vidioc-s-hw-freq-seek.xml

@@ -75,6 +75,9 @@ seek is started.</para>
 
     <para>This ioctl is supported if the <constant>V4L2_CAP_HW_FREQ_SEEK</constant> capability is set.</para>
 
+    <para>If this ioctl is called from a non-blocking filehandle, then &EAGAIN; is
+    returned and no seek takes place.</para>
+
     <table pgwide="1" frame="none" id="v4l2-hw-freq-seek">
       <title>struct <structname>v4l2_hw_freq_seek</structname></title>
       <tgroup cols="3">
@@ -157,6 +160,13 @@ one of the values in the <structfield>type</structfield>,
 fields is wrong.</para>
 	</listitem>
       </varlistentry>
+      <varlistentry>
+	<term><errorcode>EAGAIN</errorcode></term>
+	<listitem>
+	  <para>Attempted to call <constant>VIDIOC_S_HW_FREQ_SEEK</constant>
+	  with the filehandle in non-blocking mode.</para>
+	</listitem>
+      </varlistentry>
       <varlistentry>
 	<term><errorcode>ENODATA</errorcode></term>
 	<listitem>