ufshci_req_sdb_cmd_desc_construct() and ufshci_req_sdb_construct()
returned ENOMEM for every failure, so an EINVAL from bus_dma_tag_create()
was reported as a memory shortage. Capture and return the real errno,
and drop the cmd descriptor construct's now pointless out label.
No functional change: no caller inspects the value beyond propagating
it, so this only improves the diagnostics on an attach failure.
Sponsored by: Samsung Electronics