net: fec_mxc: Declare 'promisc' as bool

priv->promisc is used as the parameter of the set_promisc() call
which accepts a bool type instead of char.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>

drivers/net/fec_mxc.h

@@ -272,7 +272,7 @@ struct fec_priv {
 	struct clk clk_ref;
 	struct clk clk_ptp;
 	u32 clk_rate;
-	char promisc;
+	bool promisc;
 };
 
 /**