nfp: flower: correction of error handling

Removing reduplicated error handling when running into error path
of `nfp_compile_flow_metadata`.

Signed-off-by: Yu Xiao <yu.xiao@corigine.com>
Signed-off-by: Yinjun Zhang <yinjun.zhang@corigine.com>
Signed-off-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: David S. Miller <davem@davemloft.net>