s390/dasd: Use kzalloc instead of kmalloc/memset

Use kzalloc rather than duplicating its implementation, which
makes code simple and easy to understand.

Signed-off-by: Haowen Bai <baihaowen@meizu.com>
Reviewed-by: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Stefan Haberland <sth@linux.ibm.com>
Link: https://lore.kernel.org/r/20220505141733.1989450-6-sth@linux.ibm.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>