zram: recalculate zstd compression params once

zram: recalculate zstd compression params once

zstd compression params depends on level, but are constant
for a given instance of zstd compression backend.  Calculate
once (during ctx creation).

Link: https://lkml.kernel.org/r/20240712051850.484318-15-senozhatsky@chromium.org
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Nick Terrell <terrelln@fb.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>