buildroot

package/zlib: bump version to 1.2.10

Changed _SITE url to the upstream project site because Sourceforge does
not provide the tarball for 1.2.10 as of now.

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>