ice: Fix implicit queue mapping mode in ice_vsi_get_qs

Currently in ice_vsi_get_qs() we set the mapping_mode for Tx and Rx to
vsi->[tx|rx]_mapping_mode, but the problem is vsi->[tx|rx]_mapping_mode
have not been set yet. This was working because ICE_VSI_MAP_CONTIG is
defined to 0. Fix this by being explicit with our mapping mode by
initializing the Tx and Rx structure's mapping_mode to
ICE_VSI_MAP_CONTIG and then setting the vsi->[tx|rx]_mapping_mode to the
[tx|rx]_qs_cfg.mapping_mode values.

Also, only assign the vsi->[tx|rx]_mapping_mode when the queues are
successfully mapped to the VSI. With this change there was no longer a
need to initialize the ret variable to 0 so remove that.

Signed-off-by: Brett Creeley <brett.creeley@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>