VFIO: platform: reset: fix a warning message condition

This loop ends with count set to -1 and not zero so the warning message
isn't printed when it should be.  I've fixed this by change the postop
to a preop.

Fixes: 0990822c

 ('VFIO: platform: reset: AMD xgbe reset module')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Eric Auger <eric.auger@linaro.org>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>