media: ca-get-cap.rst: document this ioctl

Instead of a generic boilerplate, fill it with relevant
information about this ioctl.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

Documentation/media/uapi/dvb/ca-get-cap.rst

@@ -28,43 +28,17 @@ Arguments
 ``caps``
   Pointer to struct :c:type:`ca_caps`.
 
-.. c:type:: struct ca_caps
-
-.. flat-table:: struct ca_caps
-    :header-rows:  1
-    :stub-columns: 0
-
-    -
-      - type
-      - name
-      - description
-    -
-      -	unsigned int
-      - slot_num
-      - total number of CA card and module slots
-    -
-      - unsigned int
-      - slot_type
-      - bitmask with all supported slot types
-    -
-      - unsigned int
-      - descr_num
-      - total number of descrambler slots (keys)
-    -
-      - unsigned int
-      - descr_type
-      - bit mask with all supported descr types
-
-
 Description
 -----------
 
-.. note:: This ioctl is undocumented. Documentation is welcome.
-
+Queries the Kernel for information about the available CA and descrambler
+slots, and their types.
 
 Return Value
 ------------
 
-On success 0 is returned, on error -1 and the ``errno`` variable is set
+On success 0 is returned and :c:type:`ca_caps` is filled.
+
+On error, -1 is returned and the ``errno`` variable is set
 appropriately. The generic error codes are described at the
 :ref:`Generic Error Codes <gen-errors>` chapter.