iop-adma: fixup some kzalloc/memset confusions

1) Remove an explicit memset(.., 0, ...) to a variable allocated with
kzalloc (i.e. 'dest').

2) Allocate 'src' with kmalloc instead of kzalloc as all elements of the
'src' buffer are initialized in a 'for(...)' loop just after.

3) remove useless 'sizeof(u8)', which always returns 1, when computing the
size of the memory to be allocated.

Signed-off-by: Christophe Jaillet <christophe.jaillet@wanadoo.fr>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>