libata: samsung_cf: fix handling platform_get_irq result

The function can return negative value.

The problem has been detected using proposed semantic patch
scripts/coccinelle/tests/assign_signed_to_unsigned.cocci [1].

[1]: http://permalink.gmane.org/gmane.linux.kernel/2046107

Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

drivers/ata/pata_samsung_cf.c

@@ -70,7 +70,7 @@ struct s3c_ide_info {
 	struct clk *clk;
 	void __iomem *ide_addr;
 	void __iomem *sfr_addr;
-	unsigned int irq;
+	int irq;
 	enum s3c_cpu_type cpu_type;
 	unsigned int fifo_status_reg;
 };