bugfix: only push the blob id if new
bugfix: only push the blob id if new

Only push the blob id for the opened blob if this is the first time it's
been opened.

Tested: Verified it no longer just keeps growing the list every time one
opens.
Signed-off-by: Patrick Venture <36c53fa43f47f3fd67cb2fc38031827244d18a1f@google.com>
Change-Id: I1b42ce769c3c1279bdc1f7e99e8ab74c67c1427a

openbmc/phosphor-ipmi-flash