[media] conf_nitpick.py: ignore an opaque struct from v4l2-mem2mem.h

The v4l2_m2m_dev is opaque: its meaning is only known by
v4l2-mem2mem.c. Ignore it on nitpick mode.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
diff --git a/Documentation/media/conf_nitpick.py b/Documentation/media/conf_nitpick.py
index 1f3ef3d..f71bb94 100644
--- a/Documentation/media/conf_nitpick.py
+++ b/Documentation/media/conf_nitpick.py
@@ -98,4 +98,8 @@
     ("c:type", "usb_interface"),
     ("c:type", "v4l2_std_id"),
     ("c:type", "video_system_t"),
+
+    # Opaque structures
+
+    ("c:type", "v4l2_m2m_dev"),
 ]