powerpc: t1040: Correct RCW MAC2_GMII_SEL value

Per T1040RM (Rev. 1, 08/2015), the value of
FSL_CORENET_RCWSR13_MAC2_GMII_SEL_ENET_PORT is wrong
and should be 0x00000080 (bit 440 in the RCW).

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Poonam Aggrwal <poonam.aggrwal@nxp.com>
Reviewed-by: York Sun <york.sun@nxp.com>