gve: Properly handle errors in gve_assign_qpl

Ignored errors would result in crash.

Fixes: ede3fcf5 ("gve: Add support for raw addressing to the rx path")
Signed-off-by: Catherine Sullivan <csully@google.com>
Signed-off-by: Jeroen de Borst <jeroendb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>