package/valgrind: bump version to 3.16.1

* 3.16.1 fixes two critical bugs discovered after 3.16.0 was frozen.
  for details see [1].
* changed SITE from ftp to https.

[1] https://www.valgrind.org/docs/manual/dist.news.html



Signed-off-by: Michael Nosthoff <buildroot@heine.tech>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>