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>

LICENSES/deprecated/Zlib

+Valid-License-Identifier: Zlib
+SPDX-URL: https://spdx.org/licenses/Zlib.html
+Usage-Guide:
+  To use the Zlib License put the following SPDX tag/value pair into a
+  comment according to the placement guidelines in the licensing rules
+  documentation:
+    SPDX-License-Identifier: Zlib
+License-Text:
+
+zlib License
+
+Copyright (c) <year> <copyright holders>
+
+This software is provided 'as-is', without any express or implied warranty. In
+no event will the authors be held liable for any damages arising from the use
+of this software.
+
+Permission is granted to anyone to use this software for any purpose, including
+commercial applications, and to alter it and redistribute it freely, subject
+to the following restrictions:
+  1. The origin of this software must not be misrepresented; you must not
+claim that you wrote the original software. If you use this software in a
+product, an acknowledgment in the product documentation would be appreciated
+but is not required.
+  2. Altered source versions must be plainly marked as such, and must not be
+misrepresented as being the original software.
+  3. This notice may not be removed or altered from any source distribution.