kmsan: random: prevent boot-time reports in _mix_pool_bytes

Maybe it's better to zero-fill the buffer instead?

Signed-off-by: Alexander Potapenko <glider@google.com>

drivers/char/hw_random/core.c

@@ -623,6 +623,11 @@ static int __init hwrng_modinit(void)
 		kfree(rng_buffer);
 		return -ENOMEM;
 	}
+	/*
+	 * Prevent KMSAN reporting bugs when passing uninitialized data from
+	 * rng_fillbuf to mix_pool_bytes().
+	 */
+	kmsan_unpoison_shadow(rng_fillbuf, rng_buffer_size());
 
 	ret = register_miscdev();
 	if (ret) {