stmmac: fix noderef.cocci warnings

drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c:115:15-21: ERROR: application of sizeof to pointer

 sizeof when applied to a pointer typed expression gives the size of
 the pointer

Generated by: scripts/coccinelle/misc/noderef.cocci

CC: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Signed-off-by: NFengguang Wu <fengguang.wu@intel.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c

@@ -112,7 +112,7 @@ static struct stmmac_axi *stmmac_axi_setup(struct platform_device *pdev)
 	if (!np)
 		return NULL;
 
-	axi = kzalloc(sizeof(axi), GFP_KERNEL);
+	axi = kzalloc(sizeof(*axi), GFP_KERNEL);
 	if (!axi)
 		return ERR_PTR(-ENOMEM);