ARM: vic: fix build warning caused by previous commit

07c9249f (ARM: 7554/1: VIC: use irq_domain_add_simple()) removed the
use of 'irq_base' but did not remove the variable itself, which causes:

arch/arm/common/vic.c: In function 'vic_of_init':
arch/arm/common/vic.c:410:6: warning: unused variable 'irq_base'

Remove this now unused variable.
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

arch/arm/common/vic.c

@@ -407,7 +407,6 @@ void __init vic_init(void __iomem *base, unsigned int irq_start,
 int __init vic_of_init(struct device_node *node, struct device_node *parent)
 {
 	void __iomem *regs;
-	int irq_base;
 
 	if (WARN(parent, "non-root VICs are not supported"))
 		return -EINVAL;