sunvdc: don't dereference port->disk before disk probe finishes

sunvdc: don't dereference port->disk before disk probe finishes

If the backing file for a vdisk is not present in the service domain an
ldc reset can occur during the initial port/disk probing. The ldc reset
logic was dereferencing port->disk, which may not have been setup yet.
Guard against this case.

Orabug: 20362258

Signed-off-by: Chris Hyser <chris.hyser@oracle.com>
Signed-off-by: Dwight Engen <dwight.engen@oracle.com>
(cherry picked from commit cd6d3705da958b5db625272eb8733ab79a045f87)
(cherry picked from commit bee156ac9cad00f6a39417217c454085645c3d62)
(cherry picked from commit 476306db27c9a6bcd2e8012047ba06a0af16b734)
Signed-off-by: Allen Pais <allen.pais@oracle.com>