staging: kpc2000: fix error return code in kp2000_pcie_probe()

Fix to return a negative error code from the error handling
case instead of 0, as done elsewhere in this function. Also
removed var 'rv' since we can use 'err' instead.

Fixes: 7dc7967f

 ("staging: kpc2000: add initial set of Daktronics drivers")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Cc: stable <stable@vger.kernel.org>
Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/20200506134735.102041-1-weiyongjun1@huawei.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>