ravb: remove undocumented endianness selection

This patch removes the use of the undocumented BOC bit of the CCC register.

Current documentation for EtherAVB (ravb) describes the offset of what the
driver uses as the BOC bit as reserved and that only a value of 0 should be
written. After some internal investigation with Renesas it remains unclear
why this driver accesses these fields but regardless of what the historical
reasons are the current code is considered incorrect.

Based on work by Kazuya Mizuguchi <kazuya.mizuguchi.ks@renesas.com>

Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: David S. Miller <davem@davemloft.net>