octeontx2-af: Increment ptp refcount before use

Before using the ptp pci device by AF driver increment
the reference count of it.

Fixes: a8b90c9d ("octeontx2-af: Add PTP device id for CN10K and 95O silcons")
Signed-off-by: Subbaraya Sundeep <sbhatta@marvell.com>
Signed-off-by: Sunil Goutham <sgoutham@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>