mtd: nand: ams-delta: fix overwritten mtd_info->owner in initialization

In initialization routine, mtd_info->owner is overwritten by memset()
just after being initialized.  This can be fixed by moving memset() calls
to just before setting mtd_info->owner.  But the memory region is allocated
by kmalloc, so we can fix it by using kzalloc instead of kmalloc.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Jonathan McDowell <noodles@earth.li>
Cc: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>