[golan] Add explicit type casts for nodnic_queue_pair_type

[golan] Add explicit type casts for nodnic_queue_pair_type

GCC 10 emits warnings for implicit conversions of enumerated types.

The flexboot_nodnic code defines nodnic_queue_pair_type with values
identical to those of ib_queue_pair_type, and implicitly casts between
them.  Add an explicit cast to fix the warning.

Signed-off-by: Michael Brown <mcb30@ipxe.org>