[infiniband] Return status code from ib_create_cq() and ib_create_qp()

[infiniband] Return status code from ib_create_cq() and ib_create_qp()

Any underlying errors arising during ib_create_cq() or ib_create_qp()
are lost since the functions simply return NULL on error.  This makes
debugging harder, since a debug-enabled build is required to discover
the root cause of the error.

Fix by returning a status code from these functions, thereby allowing
any underlying errors to be propagated.

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