staging: crypto: skein: depend upon CRYPTO

Fengguang's randconfig kernel build tester discovered the following
warnings:

warning: (CRYPTO_THREEFISH) selects CRYPTO_ALGAPI which has unmet direct dependencies (CRYPTO)
warning: (DM_VERITY && CRYPTO_SKEIN) selects CRYPTO_HASH which has unmet direct dependencies (CRYPTO)

Fix this in the Kconfig by depending on CRYPTO.

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>
Reviewed-by: Marek Vasut <marex@denx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>