Refer to set-coding-system-priority instead of the obsolete

set-coding-priority in the doc string.

src/coding.c

@@ -10559,7 +10559,7 @@ associated with each coding-category one by one in this order.  When
 one algorithm agrees with a byte sequence of source text, the coding
 system bound to the corresponding coding-category is selected.
 
-Don't modify this variable directly, but use `set-coding-priority'.  */);
+Don't modify this variable directly, but use `set-coding-system-priority'.  */);
   {
     int i;