[media] cec-ioc-receive.rst: one table here should be longtable

The table is too big to fit into a single page on LaTeX format.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

Documentation/media/uapi/cec/cec-ioc-receive.rst

@@ -77,6 +77,8 @@ result.
 
 .. _cec-msg:
 
+.. cssclass:: longtable
+
 .. flat-table:: struct cec_msg
     :header-rows:  0
     :stub-columns: 0