mm/page-writeback: use __this_cpu_inc() in account_page_dirtied()

mm/page-writeback: use __this_cpu_inc() in account_page_dirtied()

As account_page_dirtied() was always protected by xa_lock_irqsave(), so
using __this_cpu_inc() is better.

Link: https://lkml.kernel.org/r/20210512144742.4764-1-wuchi.zero@gmail.com
Signed-off-by: Chi Wu <wuchi.zero@gmail.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Howard Cochran <hcochran@kernelspring.com>
Cc: Miklos Szeredi <mszeredi@redhat.com>
Cc: Sedat Dilek <sedat.dilek@gmail.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>