make sys_poll() wait at least timeout ms

make sys_poll() wait at least timeout ms

schedule_timeout(jiffies) waits for at least jiffies - 1.  Add 1 jiffie to
the timeout_jiffies calculated in sys_poll() to wait at least
timeout_msecs, like poll() manpage says.

Signed-off-by: Karsten Wiese <fzu@wemgehoertderstaat.de>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>