scratch parameter of log_adapter() is only used by bpck driver.
Remove it.
Reviewed-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Signed-off-by: Ondrej Zary <linux@zary.sk>
Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>