dm snapshot: free exception store on init failure

dm snapshot: free exception store on init failure

commit 034a186d29dbcef099e57ab23ec39440596be911 upstream.

While initializing the snapshot module, if we fail to register
the snapshot target then we must back-out the exception store
module initialization.

Signed-off-by: Jonathan Brassow <jbrassow@redhat.com>
Reviewed-by: Mikulas Patocka <mpatocka@redhat.com>
Reviewed-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>