[POWERPC] Fix return value check logic in debugfs virq_mapping setup

debugfs_create_file() returns a non-NULL (non-zero) value in case of
success, not a NULL value.

This fixes this non-critical boot-time debugging error message:

[    1.316386] calling  irq_debugfs_init+0x0/0x50
[    1.316399] initcall irq_debugfs_init+0x0/0x50 returned -12 after 0 msecs
[    1.316411] initcall irq_debugfs_init+0x0/0x50 returned with error code -12

Signed-off-by: Emil Medve <Emilian.Medve@Freescale.com>
Acked-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>
diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c
index 2f73f70..bcc249d 100644
--- a/arch/powerpc/kernel/irq.c
+++ b/arch/powerpc/kernel/irq.c
@@ -1073,7 +1073,7 @@
 static int __init irq_debugfs_init(void)
 {
 	if (debugfs_create_file("virq_mapping", S_IRUGO, powerpc_debugfs_root,
-				 NULL, &virq_debug_fops))
+				 NULL, &virq_debug_fops) == NULL)
 		return -ENOMEM;
 
 	return 0;