md-cluster: fix wrong condition check in raid1_write_request

The check used here is to avoid conflict between write and
resync, however we used the wrong logic, it should be the
inverse of the checking inside "if".

Fixes: 589a1c49 ("Suspend writes in RAID1 if within range")
Signed-off-by: Guoqing Jiang <gqjiang@suse.com>
Signed-off-by: Shaohua Li <shli@fb.com>