pxa168: fix double deallocation of managed resources

Commit 43d3ddf8 ("net: pxa168_eth: add device tree support") starts
to use managed resources by adding devm_clk_get() and
devm_ioremap_resource(), but it leaves explicit iounmap() and clock_put()
in pxa168_eth_remove() and in failure handling code of pxa168_eth_probe().
As a result double free can happen.

The patch removes explicit resource deallocation. Also it converts
clk_disable() to clk_disable_unprepare() to make it symmetrical with
clk_prepare_enable().

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: David S. Miller <davem@davemloft.net>