amd-xgbe: fix a couple timeout loops

At the end of the loop we test "if (!count)" but because "count--" is
a post-op then the loop will end with count set to -1.  I have fixed
this by changing it to --count.

Fixes: c5aa9e3b

 ('amd-xgbe: Initial AMD 10GbE platform driver')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>