[doc] Fixing reference inside Extended-Asm.html

[dw]

> Is the version of texinfo buggy to generate online documentation?

Sorry for the delayed response.  I was hoping the gcc expert on docs 
would respond so I could see who that was.

I have been doing some work on Extended-Asm.html (see the work in 
progress at 
http://www.limegreensocks.com/gcc/Using-Assembly-Language-with-C.html) 
and I haven't had a problem generating output.

dw