make ttyname[_r] return ENODEV rather than ENOENT

commit 0a950dcf15bb9f7274c804dca490e9e20e475f3e added checking that
the pathname a tty device was opened with actually matches the device,
which can fail to hold when a container inherits a tty from outside
the container. the error code added at the time was ENOENT; however,
discussions between affected applications and glibc developers
resulted in glibc adopting ENODEV as the error for this condition, and
this has now been documented in the man pages project as well. adopt
the same error code for consistency.

patch by Christian Brauner.

src/unistd/ttyname_r.c

@@ -23,7 +23,7 @@ int ttyname_r(int fd, char *name, size_t size)
 	if (stat(name, &st1) || fstat(fd, &st2))
 		return errno;
 	if (st1.st_dev != st2.st_dev || st1.st_ino != st2.st_ino)
-		return ENOENT;
+		return ENODEV;
 
 	return 0;
 }