Use ERR_CAST inlined function instead of ERR_PTR(PTR_ERR(...)).

drivers/net/ethernet/ti/cpts.c:567:9-16: WARNING: ERR_CAST can be used with cpts->refclk
Generated by: scripts/coccinelle/api/err_cast.cocci
Signed-off-by: Hernán Gonzalez <hernan@vanguardiasur.com.ar>
Signed-off-by: David S. Miller <davem@davemloft.net>