gve: Fix error return code in gve_alloc_qpls()

Fix to return a negative error code from the error handling
case instead of 0, as done elsewhere in this function.

Fixes: f5cedc84

 ("gve: Add transmit and receive support")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>