Ignore Device Paths in the Boot Info that don't have Media path

Ignore Device Paths in the Boot Info that don't have Media path
nodes. These show up in default entries on SuperMicro motherboards and
elsewhere. Before, we couldn't find a block device associated with the
device path and return BAD_CHOICE which was an instant
failure. However, a VendHw node isn't specifc, so when we don't find a
media path, return NOT_SPECIFIC so that the rest of the algorithms
work.

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