dm flakey: fix reads to be issued if drop_writes configured

dm flakey: fix reads to be issued if drop_writes configured

v4.8-rc3 commit 99f3c90d0d ("dm flakey: error READ bios during the
down_interval") overlooked the 'drop_writes' feature, which is meant to
allow reads to be issued rather than errored, during the down_interval.

Fixes: 99f3c90d0d ("dm flakey: error READ bios during the down_interval")
Orabug: 25444528

Reported-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Aniket Alshi <aniket.alshi@oracle.com>
Reviewed-by: Jack Vogel <jack.vogel@oracle.com>