ixgbe: fix __ixgbe_notify_dca() bail out code

The way __ixgbe_notify_dca() was currently set up it would not be
possible to add a requester. Both cases of the IXGBE_FLAG_DCA_ENABLED
bit being on and off would lead to the function exiting for a
DCA_PROVIDER_ADD.

Signed-off-by: Don Skidmore <donald.c.skidmore@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>