drivers/net/ethernet/marvell/sky2.c: fix error return code

drivers/net/ethernet/marvell/sky2.c: fix error return code

The function sky2_probe() return 0 for success and negative value
for most of its internal tests failures. There are two exceptions
that are error cases going to err_out*:. For this two cases, the
function abort its success execution path, but returns non negative
value, making it dificult for a caller function to notice the error.

This patch fixes the error cases that do not return negative values.

This was found by Coccinelle, but the code change was made by hand.
This patch is not robot generated.

A simplified version of the semantic match that finds this problem is
as follows: (http://coccinelle.lip6.fr/)

// <smpl>
(
if@p1 (\(ret < 0\|ret != 0\))
 { ... return ret; }
|
ret@p1 = 0
)
... when != ret = e1
    when != &ret
*if(...)
{
  ... when != ret = e2
      when forall
 return ret;
}
// </smpl>

Signed-off-by: Peter Senna Tschudin <peter.senna@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>