powerpc/wii: Make hlwd_pic_init function static

The function hlwd_pic_init can be made static, so do it. Fix the following
warning treated as error (W=1):

../arch/powerpc/platforms/embedded6xx/hlwd-pic.c:158:20: error: no previous prototype for ‘hlwd_pic_init’ [-Werror=missing-prototypes]
Signed-off-by: Mathieu Malaterre <malat@debian.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/platforms/embedded6xx/hlwd-pic.c

@@ -160,7 +160,7 @@ static void __hlwd_quiesce(void __iomem *io_base)
 	out_be32(io_base + HW_BROADWAY_ICR, 0xffffffff);
 }
 
-struct irq_domain *hlwd_pic_init(struct device_node *np)
+static struct irq_domain *hlwd_pic_init(struct device_node *np)
 {
 	struct irq_domain *irq_domain;
 	struct resource res;