LICENSES/deprecated: add Zlib license text

The new files contributed to zlib have Zlib SPDX license identifier. Since
there was no Zlib license text in LICENSES, scripts/spdxcheck.py
reported the following errors:
  lib/zlib_dfltcc/dfltcc.c: 1:28 Invalid License ID: Zlib
  lib/zlib_dfltcc/dfltcc.h: 1:28 Invalid License ID: Zlib
  lib/zlib_dfltcc/dfltcc_deflate.c: 1:28 Invalid License ID: Zlib
  lib/zlib_dfltcc/dfltcc_inflate.c: 1:28 Invalid License ID: Zlib
  lib/zlib_dfltcc/dfltcc_util.h: 1:28 Invalid License ID: Zlib

The patch adds Zlib SPDX license to LICENSES/deprecated, thus
resolving the issues reported by spdxcheck.

Suggested-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Reviewed-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Mikhail Zaslonko <zaslonko@linux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>