Remove the nr_exclusive argument from __wake_up_sync_key()

Remove the nr_exclusive argument from __wake_up_sync_key() and derived
functions as everything seems to set it to 1.  Note also that if it wasn't
set to 1, it would clear WF_SYNC anyway.

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>