media: lirc: fix lirc.h documentation generation

The rc_proto enum values should be ignored for now, otherwise we get
warnings like:

Documentation/output/lirc.h.rst:6: WARNING: undefined label: rc-proto-max (if the link has no caption the label must precede a section header)
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Fixes: 72e637fe ("media: rc: validate that "rc_proto" is reasonable")
Fixes: cea357bc ("media: lirc: ensure RC_PROTO_MAX has documentation")
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

Documentation/userspace-api/media/lirc.h.rst.exceptions

@@ -64,6 +64,7 @@ ignore symbol RC_PROTO_RCMM12
 ignore symbol RC_PROTO_RCMM24
 ignore symbol RC_PROTO_RCMM32
 ignore symbol RC_PROTO_XBOX_DVD
+ignore symbol RC_PROTO_MAX
 
 # Undocumented macros