dm-integrity would successfully create mappings with the number of
sectors greater than the provided data sector count.  Attempts to read
sectors of this mapping that were beyond the provided data sector count
would then yield run-time messages of the form "device-mapper:
integrity: Too big sector number: ...".

Fix this by emitting an error when the requested mapping size is bigger
than the provided data sector count.
Signed-off-by: Ondrej Mosnacek <omosnacek@gmail.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>