cam: Fail 2/0 asc/ascq return code

This asc/ascq code 2/0 ("No seek complete") is a fatal error on modern
drives indicating a sensor failure. One of our vendors noticed we
retried 2/0 so many times in their failure analysis and asked why (no
other OS else does). They've indicated that this failures means the
track couldn't be located (something that's not going to change, except
if the environment changes significantly, which won't happen on a
timescale useful to retries).

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