crypto: atmel-aes - initialize spinlock in probe

Kernel will report "BUG: spinlock lockup suspected on CPU#0"
when CONFIG_DEBUG_SPINLOCK is enabled in kernel config and the
spinlock is used at the first time. It's caused by uninitialized
spinlock, so just initialize it in probe.

Signed-off-by: Leilei Zhao <leilei.zhao@atmel.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>