zram: drop wb_limit_lock

zram: drop wb_limit_lock

We don't need wb_limit_lock.  Writeback limit setters take an exclusive
write zram init_lock, while wb_limit modifications happen only from a
single task and under zram read init_lock.  No concurrent wb_limit
modifications are possible (we permit only one post-processing task at a
time).  Add lockdep assertions to wb_limit mutators.

While at it, fixup coding styles.

Link: https://lkml.kernel.org/r/20251122074029.3948921-5-senozhatsky@chromium.org
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reviewed-by: Brian Geffon <bgeffon@google.com>
Cc: Minchan Kim <minchan@google.com>
Cc: Richard Chang <richardycc@google.com>
Cc: Yuwen Chen <ywen.chen@foxmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>