dpaa2-eth: Fix potential spectre issue

Smatch reports a potential spectre vulnerability in the dpaa2-eth
driver, where the value of rxnfc->fs.location (which is provided
from user-space) is used as index in an array.

Add a call to array_index_nospec() to sanitize the access.

Signed-off-by: Ioana Radulescu <ruxandra.radulescu@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>