__tty_open(): use the correct type for saved_flags

filp->f_flags is unsigned, so use that type for the local copy.

Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>