hwrng: core - use rng_fillbuf in add_early_randomness()

Using rng_buffer in add_early_randomness() may race with rng_dev_read().
Use rng_fillbuf instead, as it is otherwise only used within the kernel
by hwrng_fillfn() and therefore never exposed to userspace.

Cc: Matt Mackall <mpm@selenic.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/char/hw_random/core.c

@@ -66,10 +66,10 @@ static void add_early_randomness(struct hwrng *rng)
 	int bytes_read;
 
 	mutex_lock(&reading_mutex);
-	bytes_read = rng_get_data(rng, rng_buffer, 32, 0);
+	bytes_read = rng_get_data(rng, rng_fillbuf, 32, 0);
 	mutex_unlock(&reading_mutex);
 	if (bytes_read > 0)
-		add_device_randomness(rng_buffer, bytes_read);
+		add_device_randomness(rng_fillbuf, bytes_read);
 }
 
 static inline void cleanup_rng(struct kref *kref)