f2fs: compress: relocate some judgments in f2fs_reserve_compress_blocks

The following f2fs_io test will get a "0" result instead of -EINVAL,
unisoc # ./f2fs_io compress file
unisoc # ./f2fs_io reserve_cblocks file
 0
it's not reasonable, so the judgement of
atomic_read(&F2FS_I(inode)->i_compr_blocks) should be placed after
the judgement of is_inode_flag_set(inode, FI_COMPRESS_RELEASED).

Fixes: c75488fb

 ("f2fs: introduce F2FS_IOC_RESERVE_COMPRESS_BLOCKS")
Signed-off-by: Xiuhong Wang <xiuhong.wang@unisoc.com>
Signed-off-by: Zhiguo Niu <zhiguo.niu@unisoc.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>