crypto: bcm - set memory to zero only once

Use kmalloc_array() instead of kcalloc() because sg_init_table() already
sets the memory to zero. This avoids zeroing the memory twice.

Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>