crypto: qat - remove the unnecessary get_vintmsk_offset()

All QAT GEN2 devices share the same register offset for masking interrupts,
so they don't need any complex device specific infrastructure.

Remove this function in favor of a constant in order to simplify the code.
Also, future generations may require a more complex device specific
handling, making the current approach obsolete anyway.

Signed-off-by: Marco Chiappero <marco.chiappero@intel.com>
Co-developed-by: Giovanni Cabiddu <giovanni.cabiddu@intel.com>
Signed-off-by: Giovanni Cabiddu <giovanni.cabiddu@intel.com>
Reviewed-by: Fiona Trahe <fiona.trahe@intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>