ethtool: exit the loop when invalid index occurs

The commit 3de0b592 ("ethtool: Support for configurable RSS hash
key") introduced a new function ethtool_copy_validate_indir() with
full iteration of the loop to validate the ring indices, which could
be an overkill. To minimize the impact, we ought to exit the loop as
soon as the invalid index occurs for the very first time. The
remaining loop simply doesn't serve any more purpose.

Signed-off-by: Jean Sacren <sakiwit@gmail.com>
Cc: Venkata Duvvuru <VenkatKumar.Duvvuru@Emulex.Com>
Signed-off-by: David S. Miller <davem@davemloft.net>