media: cec-func-poll.rst/func-poll.rst: update EINVAL description

nfds depends on RLIMIT_NOFILE, not OPEN_MAX. Update the description
for cec and v4l2.
Signed-off-by: NHans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: NMauro Carvalho Chehab <mchehab+samsung@kernel.org>

Documentation/media/uapi/cec/cec-func-poll.rst

@@ -74,4 +74,5 @@ is returned, and the ``errno`` variable is set appropriately:
     The call was interrupted by a signal.
 
 ``EINVAL``
-    The ``nfds`` argument is greater than ``OPEN_MAX``.
+    The ``nfds`` value exceeds the ``RLIMIT_NOFILE`` value. Use
+    ``getrlimit()`` to obtain this value.

Documentation/media/uapi/v4l/func-poll.rst

@@ -113,4 +113,5 @@ EINTR
     The call was interrupted by a signal.
 
 EINVAL
-    The ``nfds`` argument is greater than ``OPEN_MAX``.
+    The ``nfds`` value exceeds the ``RLIMIT_NOFILE`` value. Use
+    ``getrlimit()`` to obtain this value.