arch/ia64/lib: Fix broken URL in comments

The URL to the book IA-64 and Elementary Functions in idiv32.S and
idiv64.S just led to a 404 page, so I updated them with a known good link
that others can reference.
Signed-off-by: Sina Hamedian <shamedian@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

arch/ia64/lib/idiv32.S

@@ -11,7 +11,7 @@
  *
  * For more details on the theory behind these algorithms, see "IA-64
  * and Elementary Functions" by Peter Markstein; HP Professional Books
- * (http://www.hp.com/go/retailbooks/)
+ * (http://www.goodreads.com/book/show/2019887.Ia_64_and_Elementary_Functions)
  */
 
 #include <asm/asmmacro.h>

arch/ia64/lib/idiv64.S

@@ -11,7 +11,7 @@
  *
  * For more details on the theory behind these algorithms, see "IA-64
  * and Elementary Functions" by Peter Markstein; HP Professional Books
- * (http://www.hp.com/go/retailbooks/)
+ * (http://www.goodreads.com/book/show/2019887.Ia_64_and_Elementary_Functions)
  */
 
 #include <asm/asmmacro.h>