dm cache: fix a harmless race when working out if a block is discarded
dm cache: fix a harmless race when working out if a block is discarded

It is more correct to hold the cell before checking the discard state.
These flags are only used as hints to the policy so this change will
have negligable effect.

Signed-off-by: Joe Thornber <61d5fad70554ae22d57a37634e04f12f58acc678@redhat.com>
Signed-off-by: Mike Snitzer <85e533f2e78486213c4d69f71462342ec0c62734@redhat.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs