net: fec: fix use-after-free in fec_drv_remove

Smatch says:
	drivers/net/ethernet/freescale/fec_main.c:3994 fec_drv_remove() error: Using fep after free_{netdev,candev}(ndev);
	drivers/net/ethernet/freescale/fec_main.c:3995 fec_drv_remove() error: Using fep after free_{netdev,candev}(ndev);

Since fep pointer is netdev private data, accessing it after free_netdev()
call can cause use-after-free bug. Fix it by moving free_netdev() call at
the end of the function

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Fixes: a31eda65 ("net: fec: fix clock count mis-match")
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
Reviewed-by: Joakim Zhang <qiangqing.zhang@nxp.com>
Reviewed-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>