tty: Fix copying of termios character map

The system termios structure and our PB
equivalent defined quite different, while
first defined as plain array we use dynamically
allocated memory. Thus the use of min() macro
is incorrect here and always produce the size of
pointer.

Fix it using the size of array from the system
provided structure. The BUILD_BUG_ON will prevent
from accidental changes.

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>