For primary VM Bus channels, primary_channel pointer is always NULL. This
pointer is valid only for the secondary channels. Also, rescind callback
is meant for primary channels only.

Fix NULL pointer dereference by retrieving the device_obj from the parent
for the primary channel.

Cc: stable@vger.kernel.org
Fixes: ca3cda6f ("uio_hv_generic: add rescind support")
Signed-off-by: Saurabh Sengar <ssengar@linux.microsoft.com>
Signed-off-by: Naman Jain <namjain@linux.microsoft.com>
Link: https://lore.kernel.org/r/20240829071312.1595-2-namjain@linux.microsoft.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>