FROMLIST: rpmsg: Guard against null endpoint ops in destroy

In RPMSG GLINK the chrdev device will allocate an ept as part of the
rpdev creation. This device will not register endpoint ops even though
it has an allocated ept. Protect against the case where the device is
being destroyed.

Bug: 163076767
Link: https://lore.kernel.org/lkml/1593017121-7953-3-git-send-email-deesin@codeaurora.org/


Change-Id: I66d9f893c3d4ed97489cba3791d540301408f0ee
Signed-off-by: Chris Lew <clew@codeaurora.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>