vt: remove uneeded retval check before tty->ops->open inside tty_open

The current check is uneeded, since !retval will always returns true,
as retval returned from tty_add_file is checked earlier and tty_open
exits if it's not zero.

Acked-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>