ice: fix function comment referring to ice_vsi_alloc

Since commit 1d2e32275de7 ("ice: split ice_vsi_setup into smaller
functions") ice_vsi_alloc has not been responsible for all of the behavior
implied by the comment for ice_vsi_setup_vector_base.

Fix the comment to refer to the new function ice_vsi_alloc_def().

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Michal Swiatkowski <michal.swiatkowski@linux.intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>