ppp: deflate: Remove useless call "zlib_inflateEnd"

Fix the following whitescan warning:

Calling "zlib_inflateEnd(&state->strm)" is only useful for its return
value, which is ignored.

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Signed-off-by: David S. Miller <davem@davemloft.net>