x86, mce: Fix compilation with !CONFIG_DEBUG_FS in mce-severity.c

Fix compilation error in arch/x86/kernel/cpu/mcheck/mce-severity.c
when CONFIG_DEBUG_FS is disabled, introduced in commit
5be9ed2.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

arch/x86/kernel/cpu/mcheck/mce-severity.c

@@ -139,6 +139,7 @@ int mce_severity(struct mce *a, int tolerant, char **msg)
 	}
 }
 
+#ifdef CONFIG_DEBUG_FS
 static void *s_start(struct seq_file *f, loff_t *pos)
 {
 	if (*pos >= ARRAY_SIZE(severities))
@@ -212,3 +213,4 @@ static int __init severities_debugfs_init(void)
 	return -ENOMEM;
 }
 late_initcall(severities_debugfs_init);
+#endif