md: use set_bit/clear_bit instead of shift/mask for bi_flags changes.

Using {set,clear}_bit is more consistent than shifting and masking.

No functional change.

Signed-off-by: NeilBrown <neilb@suse.de>

diff --cc drivers/md/raid1.c
Simple merge

diff --cc drivers/md/raid10.c
Simple merge

diff --cc drivers/md/raid5.c
Simple merge