net: cpsw: check for cpts pointer after its allocation

after priv->cpts got allocated then this pointer should check to determine
if the allocation succeeded or not.

Cc: Mugunthan V N <mugunthanvnm@ti.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: David S. Miller <davem@davemloft.net>