f2fs: fix macro definition stat_inc_cp_count

The macro stat_inc_cp_count accepts a parameter si,
but it was not used, rather the variable sbi was directly used,
which may be a local variable inside a function that calls the macros.

Signed-off-by: Julian Sun <sunjunchao2870@gmail.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>