f2fs: compress: fix to set zstd compress level correctly

f2fs: compress: fix to set zstd compress level correctly

As 5kft reported in [1]:

set_compress_context() should set compress level into .i_compress_flag
for zstd as well as lz4hc, otherwise, zstd compressor will still use
default zstd compress level during compression, fix it.

[1] https://lore.kernel.org/linux-f2fs-devel/8e29f52b-6b0d-45ec-9520-e63eb254287a@www.fastmail.com/T/#u

Fixes: 2bb9b2744764 ("f2fs: compress: support compress level")
Reported-by: 5kft <5kft@5kft.org>
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>