lib/zlib: remove redundation assignement of avail_in dfltcc_gdht()

lib/zlib: remove redundation assignement of avail_in dfltcc_gdht()

cppcheck reports
lib/zlib_dfltcc/dfltcc_deflate.c:65:21: warning: Redundant assignment of 'avail_in' to itself. [selfAssignment]
    size_t avail_in = avail_in = strm->avail_in;

Only setting avail_in once is needed.

Link: https://lkml.kernel.org/r/20230128165048.1245792-1-trix@redhat.com
Fixes: aa5b395b69b6 ("lib/zlib: add s390 hardware support for kernel zlib_deflate")
Signed-off-by: Tom Rix <trix@redhat.com>
Acked-by: Ilya Leoshkevich <iii@linux.ibm.com>
Acked-by: Mikhail Zaslonko <zaslonko@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>