i40e: Fix wrong mask used during DCB config

i40e: Fix wrong mask used during DCB config

Mask used for clearing PRTDCB_RETSTCC register in function
i40e_dcb_hw_rx_ets_bw_config() is incorrect as there is used
define I40E_PRTDCB_RETSTCC_ETSTC_SHIFT instead of define
I40E_PRTDCB_RETSTCC_ETSTC_MASK.

The PRTDCB_RETSTCC register is used to configure whether ETS
or strict priority is used as TSA in Rx for particular TC.

In practice it means that once the register is set to use ETS
as TSA then it is not possible to switch back to strict priority
without CoreR reset.

Fix the value in the clearing mask.

Fixes: 90bc8e003be2 ("i40e: Add hardware configuration for software based DCB")
Signed-off-by: Ivan Vecera <ivecera@redhat.com>
Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Tested-by: Pucha Himasekhar Reddy <himasekharx.reddy.pucha@intel.com> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>