mm/kmemleak.c: fix unused-function warning

The only references outside of the #ifdef have been removed, so now we
get a warning in non-SMP configurations:

  mm/kmemleak.c:1404:13: error: unused function 'scan_large_block' [-Werror,-Wunused-function]

Add a new #ifdef around it.

Link: http://lkml.kernel.org/r/20190416123148.3502045-1-arnd@arndb.de
Fixes: 298a32b132 ("kmemleak: powerpc: skip scanning holes in the .bss section")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Vincent Whitchurch <vincent.whitchurch@axis.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/kmemleak.c

@@ -1401,6 +1401,7 @@ static void scan_block(void *_start, void *_end,
 /*
  * Scan a large memory block in MAX_SCAN_SIZE chunks to reduce the latency.
  */
+#ifdef CONFIG_SMP
 static void scan_large_block(void *start, void *end)
 {
 	void *next;
@@ -1412,6 +1413,7 @@ static void scan_large_block(void *start, void *end)
 		cond_resched();
 	}
 }
+#endif
 
 /*
  * Scan a memory block corresponding to a kmemleak_object. A condition is