fs-verity: use u64_to_user_ptr()

<linux/kernel.h> already provides a macro u64_to_user_ptr().
Use it instead of open-coding the two casts.

No change in behavior.

Link: https://lore.kernel.org/r/20191231175408.20524-1-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>

fs/verity/enable.c

@@ -216,8 +216,7 @@ static int enable_verity(struct file *filp,
 
 	/* Get the salt if the user provided one */
 	if (arg->salt_size &&
-	    copy_from_user(desc->salt,
-			   (const u8 __user *)(uintptr_t)arg->salt_ptr,
+	    copy_from_user(desc->salt, u64_to_user_ptr(arg->salt_ptr),
 			   arg->salt_size)) {
 		err = -EFAULT;
 		goto out;
@@ -226,8 +225,7 @@ static int enable_verity(struct file *filp,
 
 	/* Get the signature if the user provided one */
 	if (arg->sig_size &&
-	    copy_from_user(desc->signature,
-			   (const u8 __user *)(uintptr_t)arg->sig_ptr,
+	    copy_from_user(desc->signature, u64_to_user_ptr(arg->sig_ptr),
 			   arg->sig_size)) {
 		err = -EFAULT;
 		goto out;