net: qmi_wwan: ignore bogus CDC Union descriptors

The CDC descriptors found on these vendor specific functions should
not be considered authoritative.  They seem to be ignored by drivers
for other systems, and the quality is therefore low.

One device (1e0e:9001) has been reported to have such a bogus union
descriptor on the QMI function, making it fail probing even if the
device id was dynamically added.  The report was not complete enough
to allow adding a device entry for this modem. But this should at
least fix the dynamic id probing problem.

Reported-by: Kanerva Topi <Topi.Kanerva@cinia.fi>
Signed-off-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: David S. Miller <davem@davemloft.net>