ptp: vmclock: Set driver data before its usage

If vmclock_ptp_register() fails during probing, vmclock_remove() is
called to clean up the ptp clock and misc device.
It uses dev_get_drvdata() to access the vmclock state.
However the driver data is not yet set at this point.

Assign the driver data earlier.

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