ARM: fix bug of checking on signed return value using unsigned statement in w90p910 platform

To fix the bug of checking on signed return value using unsigned statement.
Thanks Roel Kluin for digging out it.

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Signed-off-by: Wan ZongShun <mcuos.com@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/arm/w90p910_ether.c

@@ -160,8 +160,8 @@ struct  w90p910_ether {
 	struct mii_if_info mii;
 	struct timer_list check_timer;
 	void __iomem *reg;
-	unsigned int rxirq;
-	unsigned int txirq;
+	int rxirq;
+	int txirq;
 	unsigned int cur_tx;
 	unsigned int cur_rx;
 	unsigned int finish_tx;