f2fs: compress: fix to cover {reserve,release}_compress_blocks() w/ cp_rwsem lock

f2fs: compress: fix to cover {reserve,release}_compress_blocks() w/ cp_rwsem lock

It needs to cover {reserve,release}_compress_blocks() w/ cp_rwsem lock
to avoid racing with checkpoint, otherwise, filesystem metadata including
blkaddr in dnode, inode fields and .total_valid_block_count may be
corrupted after SPO case.

Fixes: ef8d563f184e ("f2fs: introduce F2FS_IOC_RELEASE_COMPRESS_BLOCKS")
Fixes: c75488fb4d82 ("f2fs: introduce F2FS_IOC_RESERVE_COMPRESS_BLOCKS")
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>