media: rc docs: fix warning for RC_PROTO_IMON

This protocol was recently added and causes warnings.
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

Documentation/media/lirc.h.rst.exceptions

@@ -57,6 +57,7 @@ ignore symbol RC_PROTO_RC6_MCE
 ignore symbol RC_PROTO_SHARP
 ignore symbol RC_PROTO_XMP
 ignore symbol RC_PROTO_CEC
+ignore symbol RC_PROTO_IMON
 
 # Undocumented macros