Simplify BDA::device_identifiers body
Simplify BDA::device_identifiers body

It passes the result from setup() through w/out change unless a static
header was succesfully read. This way, our code only handles the
interesting case, leaving the rest to well known methods of the Option
and Result types.

Signed-off-by: mulhern <7b51bcf507bcd7afb72bf8663752c0ddbeb517f6@redhat.com>

stratis-storage/stratisd,stratis-storage/stratisd,stratis-storage/stratisd