lib: correct link to the original source for div64_u64

The code refers to an invalid url
http://www.hackersdelight.org/HDcode/newCode/divDouble.c.txt

The correct url is
http://www.hackersdelight.org/hdcodetxt/divDouble.c.txt



Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>