lib/zlib: DFLTCC deflate does not write all available bits for Z_NO_FLUSH

lib/zlib: DFLTCC deflate does not write all available bits for Z_NO_FLUSH

DFLTCC deflate with Z_NO_FLUSH might generate a corrupted stream when the
output buffer is not large enough to fit all the deflate output at once.
The problem takes place on closing the deflate block since flush_pending()
might leave some output bits not written.  Similar problem for software
deflate with Z_BLOCK flush option (not supported by kernel zlib deflate)
has been fixed a while ago in userspace zlib but the fix never got to the
kernel.

Now flush_pending() flushes the bit buffer before copying out the byte
buffer, in order to really flush as much as possible.

Currently there are no users of DFLTCC deflate with Z_NO_FLUSH option in
the kernel so the problem remained hidden for a while.

This commit is based on the old zlib commit:
https://github.com/madler/zlib/commit/0b828b4

Link: https://lkml.kernel.org/r/20230221131617.3369978-2-zaslonko@linux.ibm.com
Signed-off-by: Mikhail Zaslonko <zaslonko@linux.ibm.com>
Acked-by: Ilya Leoshkevich <iii@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>