crypto: dh - Remove the unused function dh_safe_prime_dh_alg()

Fix the following W=1 kernel warnings:

crypto/dh.c:311:31: warning: unused function 'dh_safe_prime_dh_alg'
[-Wunused-function]
Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/dh.c

@@ -308,12 +308,6 @@ static inline struct dh_safe_prime_instance_ctx *dh_safe_prime_instance_ctx(
 	return kpp_instance_ctx(kpp_alg_instance(tfm));
 }
 
-static inline struct kpp_alg *dh_safe_prime_dh_alg(
-	struct dh_safe_prime_tfm_ctx *ctx)
-{
-	return crypto_kpp_alg(ctx->dh_tfm);
-}
-
 static int dh_safe_prime_init_tfm(struct crypto_kpp *tfm)
 {
 	struct dh_safe_prime_instance_ctx *inst_ctx =