ixgbe: use correct mask when enabling sriov

Swap the parameters in GENMASK in order to generate the correct mask.

This change fixes Tx hangs when enabling SRIOV.

Signed-off-by: Emil Tantilov <emil.s.tantilov@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>