ANDROID: GKI: scripts: Makefile: update the lz4 command (#2)

When the command was switched over from 'lz4c' to 'lz4', it changed the
meaning of '-c' in a subtle way. In the older lz4c tool, this '-cX'
seems to be a different flag, meaning the compression level. In the
newer lz4 tool, it means to compress to stdout. However, since kbuild
already specifies stdout as a file name, '-c' is superfluous, and
generates a warning:

Warning : stdout won't be used ! Do you want multiple input files (-m) ?

Fix it by removing the extra stdout flag.

Bug: 159285792
Bug: 160031736
Test: build/build.sh
Signed-off-by: Alistair Delva <adelva@google.com>
Change-Id: I96247317ccb31f224c6a8e6e453cddde5e0c2550