f2fs: allocate proper size memory for zstd decompress

As 5kft <5kft@5kft.org> reported:

 kworker/u9:3: page allocation failure: order:9, mode:0x40c40(GFP_NOFS|__GFP_COMP), nodemask=(null),cpuset=/,mems_allowed=0
 CPU: 3 PID: 8168 Comm: kworker/u9:3 Tainted: G         C        5.8.3-sunxi #trunk
 Hardware name: Allwinner sun8i Family
 Workqueue: f2fs_post_read_wq f2fs_post_read_work
 [<c010d6d5>] (unwind_backtrace) from [<c0109a55>] (show_stack+0x11/0x14)
 [<c0109a55>] (show_stack) from [<c056d489>] (dump_stack+0x75/0x84)
 [<c056d489>] (dump_stack) from [<c0243b53>] (warn_alloc+0xa3/0x104)
 [<c0243b53>] (warn_alloc) from [<c024473b>] (__alloc_pages_nodemask+0xb87/0xc40)
 [<c024473b>] (__alloc_pages_nodemask) from [<c02267c5>] (kmalloc_order+0x19/0x38)
 [<c02267c5>] (kmalloc_order) from [<c02267fd>] (kmalloc_order_trace+0x19/0x90)
 [<c02267fd>] (kmalloc_order_trace) from [<c047c665>] (zstd_init_decompress_ctx+0x21/0x88)
 [<c047c665>] (zstd_init_decompress_ctx) from [<c047e9cf>] (f2fs_decompress_pages+0x97/0x228)
 [<c047e9cf>] (f2fs_decompress_pages) from [<c045d0ab>] (__read_end_io+0xfb/0x130)
 [<c045d0ab>] (__read_end_io) from [<c045d141>] (f2fs_post_read_work+0x61/0x84)
 [<c045d141>] (f2fs_post_read_work) from [<c0130b2f>] (process_one_work+0x15f/0x3b0)
 [<c0130b2f>] (process_one_work) from [<c0130e7b>] (worker_thread+0xfb/0x3e0)
 [<c0130e7b>] (worker_thread) from [<c0135c3b>] (kthread+0xeb/0x10c)
 [<c0135c3b>] (kthread) from [<c0100159>]

zstd may allocate large size memory for {,de}compression, it may cause
file copy failure on low-end device which has very few memory.

For decompression, let's just allocate proper size memory based on current
file's cluster size instead of max cluster size.

Reported-by: 5kft <5kft@5kft.org>
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>