irqchip/qcom: Fix u32 comparison with value less than zero

The comparison of u32 nregs being less than zero is never true since
nregs is unsigned. Fix this by making nregs a signed integer.

Fixes: f20cc9b00c ("irqchip/qcom: Add IRQ combiner driver")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: kernel-janitors@vger.kernel.org
Cc: Jason Cooper <jason@lakedaemon.net>
Link: https://lkml.kernel.org/r/20171117183553.2739-1-colin.king@canonical.com

drivers/irqchip/qcom-irq-combiner.c

@@ -238,7 +238,7 @@ static int __init combiner_probe(struct platform_device *pdev)
 {
 	struct combiner *combiner;
 	size_t alloc_sz;
-	u32 nregs;
+	int nregs;
 	int err;
 
 	nregs = count_registers(pdev);