trivial: try harder to make sure mtdram is set up
trivial: try harder to make sure mtdram is set up

the autopkgtest environment in Ubuntu seems to not be preparing the mtdram
device properly. Sometimes the udev node "exists" but the /dev/mtd0 does not
exist.

Look for this explicitly and skip the test if it happens.

fwupd/fwupd,fwupd/fwupd,fwupd/fwupd,fwupd/fwupd