ptp: vmclock: Add .owner to vmclock_miscdev_fops

Without the .owner field, the module can be unloaded while /dev/vmclock0
is open, leading to an oops.

Fixes: 20503272 ("ptp: Add support for the AMZNC10C 'vmclock' device")
Cc: stable@vger.kernel.org
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>