ibmvnic: Fix RX queue buffer cleanup

[ Upstream commit b7cdec3d699db2e5985ad39de0f25d3b6111928e ]

The wrong index is used when cleaning up RX buffer objects during release
of RX queues. Update to use the correct index counter.

Signed-off-by: Thomas Falcon <tlfalcon@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>