crypto: sun4i-ss - mark sun4i_hash() static

We get 1 warning when building kernel with W=1:
drivers/crypto/sunxi-ss/sun4i-ss-hash.c:168:5: warning: no previous prototype for 'sun4i_hash' [-Wmissing-prototypes]

In fact, this function is only used in the file in which it is
declared and don't need a declaration, but can be made static.
So this patch marks it 'static'.

Signed-off-by: Baoyou Xie <baoyou.xie@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>