crypto: ux500/hash - Prepare clock before enabling it

If we fail to prepare the ux500-hash clock before enabling it the
platform will fail to boot. Here we insure this happens.

Cc: David S. Miller <davem@davemloft.net>
Cc: Andreas Westin <andreas.westin@stericsson.com>
Cc: linux-crypto@vger.kernel.org
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>