crypto: rng - Remove unused function __crypto_rng_cast()

This fixes the following warning when building with clang:

crypto/rng.c:35:34: error: unused function '__crypto_rng_cast'
    [-Werror,-Wunused-function]
Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/rng.c

@@ -33,11 +33,6 @@ struct crypto_rng *crypto_default_rng;
 EXPORT_SYMBOL_GPL(crypto_default_rng);
 static int crypto_default_rng_refcnt;
 
-static inline struct crypto_rng *__crypto_rng_cast(struct crypto_tfm *tfm)
-{
-	return container_of(tfm, struct crypto_rng, base);
-}
-
 int crypto_rng_reset(struct crypto_rng *tfm, const u8 *seed, unsigned int slen)
 {
 	u8 *buf = NULL;