sfc_ef100: potential dereference of null pointer

The return value of kmalloc() needs to be checked.
To avoid use in efx_nic_update_stats() in case of the failure of alloc.

Fixes: b593b6f ("sfc_ef100: statistics gathering")
Signed-off-by: Jiasheng Jiang <jiasheng@iscas.ac.cn>

drivers/net/ethernet/sfc/ef100_nic.c

@@ -602,6 +602,9 @@ static size_t ef100_update_stats(struct efx_nic *efx,
 				 struct rtnl_link_stats64 *core_stats)
 {
 	__le64 *mc_stats = kmalloc(array_size(efx->num_mac_stats, sizeof(__le64)), GFP_ATOMIC);
+	if (!mc_stats)
+		return 0;
+
 	struct ef100_nic_data *nic_data = efx->nic_data;
 	DECLARE_BITMAP(mask, EF100_STAT_COUNT) = {};
 	u64 *stats = nic_data->stats;