octeontx2-pf: Add check for non zero mcam flows

This patch ensures that mcam flows are allocated
before adding or destroying the flows.

Signed-off-by: Sunil Goutham <sgoutham@marvell.com>
Signed-off-by: Subbaraya Sundeep <sbhatta@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>