crypto: talitos - reorder code in talitos_edesc_alloc()

This patch moves the mapping of IV after the kmalloc(). This
avoids having to unmap in case kmalloc() fails.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Reviewed-by: Horia Geantă <horia.geanta@nxp.com>
Cc: stable@vger.kernel.org
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>