[MIPS] au1x00_eth.c: Fix au1x00_miiphy_{read,write} build error

[MIPS] au1x00_eth.c: Fix au1x00_miiphy_{read,write} build error

au1x00_eth.c: In function 'au1x00_enet_initialize':
au1x00_eth.c:246: error: 'au1x00_miiphy_read' undeclared (first use in this function)
au1x00_eth.c:246: error: (Each undeclared identifier is reported only once
au1x00_eth.c:246: error: for each function it appears in.)
au1x00_eth.c:246: error: 'au1x00_miiphy_write' undeclared (first use in this function)
au1x00_eth.c: In function 'au1x00_miiphy_write':
au1x00_eth.c:298: warning: 'return' with no value, in function returning non-void
make[1]: *** [au1x00_eth.o] Error 1

Fixed by moving these two functions forward.

Signed-off-by: Shinya Kuribayashi <skuribay@ruby.dti.ne.jp>