octeontx2-pf: Fix pfc_alloc_status array overflow

This patch addresses pfc_alloc_status array overflow occurring for
send queue index value greater than PFC priority. Queue index can be
greater than supported PFC priority for multiple scenarios (e.g. QoS,
during non zero SMQ allocation for a PF/VF).
In those scenarios the API should return default tx scheduler '0'.
This is causing mbox errors as otx2_get_smq_idx returing invalid smq value.

Fixes: 99c969a8 ("octeontx2-pf: Add egress PFC support")
Signed-off-by: Suman Ghosh <sumang@marvell.com>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>