ice: Fix potential return of uninitialized value

In ice_vsi_setup_[tx|rx]_rings, err is uninitialized which can result in
a garbage value return to the caller. Fix that.

Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Anirudh Venkataramanan <anirudh.venkataramanan@intel.com>
Tested-by: Tony Brelinski <tonyx.brelinski@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>