percpu: kill compile warning in pcpu_populate_chunk()

Impact: remove compile warning

Mark local variable map_end in pcpu_populate_chunk() with
uninitialized_var().  The variable is always used in tandem with
map_start and guaranteed to be initialized before use but gcc doesn't
understand that.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Ingo Molnar <mingo@elte.hu>

mm/percpu.c

@@ -639,7 +639,7 @@ static int pcpu_populate_chunk(struct pcpu_chunk *chunk, int off, int size)
 	int page_start = PFN_DOWN(off);
 	int page_end = PFN_UP(off + size);
 	int map_start = -1;
-	int map_end;
+	int uninitialized_var(map_end);
 	unsigned int cpu;
 	int i;