octeontx2-af: Move validation of ptp pointer before its usage

Moved PTP pointer validation before its use to avoid smatch warning.
Also used kzalloc/kfree instead of devm_kzalloc/devm_kfree.

Fixes: 2ef4e45d ("octeontx2-af: Add PTP PPS Errata workaround on CN10K silicon")
Signed-off-by: Naveen Mamindlapalli <naveenm@marvell.com>
Signed-off-by: Sunil Goutham <sgoutham@marvell.com>
Signed-off-by: Sai Krishna <saikrishnag@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>