Correct return codes during racy destruction.

Correct return codes during racy destruction.

Errors in PnP retun codes found when testing under driver
verifier with mixed VM lifecycle operations. Under some
rare cases, it is possible to get more than one PnP
"remove-like" operation. This results in a PnP remove
operation being processed whilst the device is already
in the deleted state.

This patch fixes the immediate cause of the bugfixes,
by fixing the return code. Device destruction is
unchanged. Investigation into the root cause is still
ongoing.

Signed-off-by: Martin Harvey <martin.harvey@citrix.com>
Cosmetic fixes.

Signed-off-by: Paul Durrant <paul@xen.org>