dm cache: move hook_info into common portion of per_bio_data structure
dm cache: move hook_info into common portion of per_bio_data structure

Commit c9d28d5d ("dm cache: promotion optimisation for writes")
incorrectly placed the 'hook_info' member in the writethrough-only
portion of the per_bio_data structure.

Given that the overwrite optimization may be used for writeback the
'hook_info' member must be placed above the 'cache' member of the
per_bio_data structure.  Any members above 'cache' are available from
both writeback and writethrough modes' per_bio_data structure.

Signed-off-by: Mike Snitzer <85e533f2e78486213c4d69f71462342ec0c62734@redhat.com>
Acked-by: Joe Thornber <61d5fad70554ae22d57a37634e04f12f58acc678@redhat.com>
Cc: 4fbacc2fa0ffdbb11bf1ad6925b886ebd08dd15f@vger.kernel.org # 3.13+

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