pipe: return -ENOIOCTLCMD instead of -EINVAL on unknown ioctl command

As described in commit 07d106d0 ("vfs: fix up ENOIOCTLCMD error
handling"), drivers should return -ENOIOCTLCMD if they receive an ioctl
command which they don't understand. Doing so will result in -ENOTTY
being returned to userspace, which matches the behaviour of the compat
layer if it fails to translate an ioctl command.

This patch fixes the pipe ioctl to return -ENOIOCTLCMD instead of
-EINVAL when passed an unknown ioctl command.

Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/pipe.c

@@ -693,7 +693,7 @@ static long pipe_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 
 			return put_user(count, (int __user *)arg);
 		default:
-			return -EINVAL;
+			return -ENOIOCTLCMD;
 	}
 }