tty: define tty_open_by_driver when CONFIG_TTY is not defined

[Okash Khawaja <okash.khawaja@gmail.com>]

This patch adds definition of tty_open_by_driver when CONFIG_TTY is not
defined. This was supposed to have been included in commit
12e84c71b7d4ee38d51377fd494ac748ee4e6912 ("tty: export
tty_open_by_driver"). The patch follows convention for other such
functions and returns NULL.

Signed-off-by: Okash Khawaja <okash.khawaja@gmail.com>

---
 include/linux/tty.h |    3 +++
 1 file changed, 3 insertions(+)

--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -422,6 +422,9 @@ static inline int __init tty_init(void)
 { return 0; }
 static inline const char *tty_name(const struct tty_struct *tty)
 { return "(none)"; }
+static struct tty_struct *tty_open_by_driver(dev_t device, struct inode *inode,
+		struct file *filp)
+{ return NULL; }
 #endif
 
 extern struct ktermios tty_std_termios;