ptp: vmclock: Don't unregister misc device if it was not registered

vmclock_remove() tries to detect the successful registration of the misc
device based on the value of its minor value.
However that check is incorrect if the misc device registration was not
attempted in the first place.

Always initialize the minor number, so the check works properly.

Fixes: 2050327 ("ptp: Add support for the AMZNC10C 'vmclock' device")
Cc: stable@vger.kernel.org
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Author: t-8ch

drivers/ptp/ptp_vmclock.c

@@ -550,14 +550,15 @@ static int vmclock_probe(struct platform_device *pdev)
 		goto out;
 	}
 
+	st->miscdev.minor = MISC_DYNAMIC_MINOR;
+
 	/*
 	 * If the structure is big enough, it can be mapped to userspace.
 	 * Theoretically a guest OS even using larger pages could still
 	 * use 4KiB PTEs to map smaller MMIO regions like this, but let's
 	 * cross that bridge if/when we come to it.
 	 */
 	if (le32_to_cpu(st->clk->size) >= PAGE_SIZE) {
-		st->miscdev.minor = MISC_DYNAMIC_MINOR;
 		st->miscdev.fops = &vmclock_miscdev_fops;
 		st->miscdev.name = st->name;