scripts/gen_initramfs_list.sh: fix flags for initramfs LZ4 compression

LZ4 as implemented in the kernel differs from the default method now
used by the reference implementation of LZ4.  Until the in-kernel method
is updated to support the new default, passing the legacy flag (-l) to
the compressor is necessary.  Without this flag the kernel-generated,
LZ4-compressed initramfs is junk.

Kyungsik said:

: It seems that lz4 supports legacy format with the same option as lz4c
: does.  Just looking at the first few bytes of lz4 compressed image, we can
: see whether it is new format or not.
:
: It shows new format magic number without this patch.  New format magic
: number is 0x184d2204.
:
: $ hexdump -C ./initramfs_data.cpio.lz4 |more
: 00000000  04 22 4d 18 64 70 b9 69 (Little Endian)
: ...
:
: Currently kernel supports legacy format only.
Signed-off-by: Daniel M. Weeks <dan@danweeks.net>
Cc: Michal Marek <mmarek@suse.cz>
Acked-by: Kyungsik Lee <kyungsik.lee@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/gen_initramfs_list.sh

@@ -257,7 +257,7 @@ case "$arg" in
                 && compr="lzop -9 -f"
 		echo "$output_file" | grep -q "\.lz4$" \
                 && [ -x "`which lz4 2> /dev/null`" ] \
-                && compr="lz4 -9 -f"
+                && compr="lz4 -l -9 -f"
 		echo "$output_file" | grep -q "\.cpio$" && compr="cat"
 		shift
 		;;