doc-rst: parse-headers: don't do substituition references

Add one extra escape character to avoid those warnings:
	Documentation/linux_tv/videodev2.h.rst:6: WARNING: Inline substitution_reference start-string without end-string.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

Documentation/sphinx/parse-headers.pl

@@ -220,7 +220,7 @@ $data =~ s/\n\s+\n/\n\n/g;
 #
 # Add escape codes for special characters
 #
-$data =~ s,([\_\`\*\<\>\&\\\\:\/]),\\$1,g;
+$data =~ s,([\_\`\*\<\>\&\\\\:\/\|]),\\$1,g;
 
 $data =~ s,DEPRECATED,**DEPRECATED**,g;