dm-integrity: fix a typo in the code for write/discard race

dm-integrity: fix a typo in the code for write/discard race

If we send a write followed by a discard, it may be possible that the
discarded data end up being overwritten by the previous write from the
journal. The code tries to prevent that, but there was a typo in this
logic that made it not being activated as it should be.

Note that if we end up here the second time (when discard_retried is
true), it means that the write bio is actually racing with the discard
bio, and in this situation it is not specified which of them should win.

Cc: stable@vger.kernel.org
Fixes: 31843edab7cb ("dm integrity: improve discard in journal mode")
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>