net: fec: fix unbalanced clk disable on driver unbind

When the driver is removed (e.g. using unbind through sysfs), the
clocks get disabled twice, once on fec_enet_close and once on
fec_drv_remove. Since the clocks are enabled only once, this leads
to a warning:

WARNING: CPU: 0 PID: 402 at drivers/clk/clk.c:992 clk_core_disable+0x64/0x68()

Remove the call to fec_enet_clk_enable in fec_drv_remove to balance
the clock enable/disable calls again. This has been introduce by
e8fcfcd5 ("net: fec: optimize the clock management to save power").

Signed-off-by: Stefan Agner <stefan@agner.ch>
Acked-by: Fugang Duan <B38611@freescale.com>
Signed-off-by: David S. Miller <davem@davemloft.net>