[depr.c.macros] Update to refer to C23 5.3.5.3.3, 7.33.6

... due to new sections added after WG14 N3220

Author: frederick-vs-ja

source/future.tex

@@ -230,7 +230,7 @@
 The header defines these macros the same as
 the C standard library header \libheader{float.h}.
 
-\xrefc{5.2.4.2.2, 7.33.5}
+\xrefc{5.3.5.3.3, 7.33.6}
 
 \pnum
 In addition to being available via inclusion of the \libheader{cfloat} header,