net: phy: Set SUPPORTED_1000baseX_Half flag in ESTATUS_1000_XHALF case

Commit de1d786e (add support for Xilinx 1000BASE-X phy (GTX)) introduced the
checking for ESTATUS_1000_XHALF, but it incorrectly sets the
SUPPORTED_1000baseX_Full flag in this case.

Set the SUPPORTED_1000baseX_Half flag instead.

Acked-by: Charles Coldwell <coldwell@gmail.com>
Reviewed-By: Sascha Silbe <t-uboot@infra-silbe.de>
Reviewed-by: Joe Hershberger <joe.hershberger@ni.com>
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>