As the kemdup could return NULL, it should be better to check the return
value and return error if fails.
Moreover, the return value of prestera_acl_ruleset_keymask_set() should
be checked by cascade.

Fixes: 604ba230 ("net: prestera: flower template support")
Signed-off-by: NJiasheng Jiang <jiasheng@iscas.ac.cn>
Reviewed-by: Taras Chornyi<tchornyi@marvell.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>