x86/doc: Fix the 'tlb_single_page_flush_ceiling' sysconfig path

Fix the documented sysconfig location of 'tlb_single_page_flush_ceiling'
which is under /sys/kernel/debug/... not /sys/debug/kernel/...

Signed-off-by: Jeremiah Mahler <jmmahler@gmail.com>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Link: http://lkml.kernel.org/r/1407484195-1441-1-git-send-email-jmmahler@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

Documentation/x86/tlb.txt

@@ -35,7 +35,7 @@ invlpg instruction (or instructions _near_ it) show up high in
 profiles.  If you believe that individual invalidations being
 called too often, you can lower the tunable:
 
-	/sys/debug/kernel/x86/tlb_single_page_flush_ceiling
+	/sys/kernel/debug/x86/tlb_single_page_flush_ceiling
 
 This will cause us to do the global flush for more cases.
 Lowering it to 0 will disable the use of the individual flushes.