fscrypt: Include <linux/once.h> in fs/crypto/keyring.c

Include <linux/once.h> header to allow the removal of legacy
inclusion of <linux/prandom.h> from <linux/random.h>.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Cc: Theodore Y. Ts'o <tytso@mit.edu>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Acked-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

Author: ubizjak

fs/crypto/keyring.c

@@ -22,6 +22,7 @@
 #include <crypto/skcipher.h>
 #include <linux/key-type.h>
 #include <linux/random.h>
+#include <linux/once.h>
 #include <linux/seq_file.h>
 
 #include "fscrypt_private.h"