ar71xx: rb91x: fix pll_1000 value for eth0 to avoid packet loss

When the RB91x device uses a GbE link the connection
suffers from packet loss:

  root@OpenWrt:/# ping 192.168.1.254 -s 65507 -c 20 -q
  PING 192.168.1.254 (192.168.1.254): 65507 data bytes

  --- 192.168.1.254 ping statistics ---
  20 packets transmitted, 9 packets received, 55% packet loss
  round-trip min/avg/max = 4.570/4.815/4.999 ms

Using a different PLL value fixes the issue.

  root@OpenWrt:/# ping 192.168.1.254 -s 65507 -c 100 -q
  PING 192.168.1.254 (192.168.1.254): 65507 data bytes

  --- 192.168.1.254 ping statistics ---
  100 packets transmitted, 100 packets received, 0% packet loss
  round-trip min/avg/max = 4.449/5.413/13.870 ms

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>

SVN-Revision: 39642