blkio: fix for modular blk-cgroup build

After merging the block tree, 20100414's linux-next build (x86_64
allmodconfig) failed like this:

ERROR: "get_gendisk" [block/blk-cgroup.ko] undefined!
ERROR: "sched_clock" [block/blk-cgroup.ko] undefined!

This happens because the two symbols aren't exported and hence not available
when blk-cgroup code is built as a module. I've tried to stay consistent with
the use of EXPORT_SYMBOL or EXPORT_SYMBOL_GPL with the other symbols in the
respective files.
Signed-off-by: Divyesh Shah <dpshah@google.com>
Acked-by: Gui Jianfeng <guijianfeng@cn.fujitsu.cn>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

block/genhd.c

@@ -596,6 +596,7 @@ struct gendisk *get_gendisk(dev_t devt, int *partno)
 
 	return disk;
 }
+EXPORT_SYMBOL(get_gendisk);
 
 /**
  * bdget_disk - do bdget() by gendisk and partition number

kernel/sched_clock.c

@@ -41,6 +41,7 @@ unsigned long long __attribute__((weak)) sched_clock(void)
 	return (unsigned long long)(jiffies - INITIAL_JIFFIES)
 					* (NSEC_PER_SEC / HZ);
 }
+EXPORT_SYMBOL_GPL(sched_clock);
 
 static __read_mostly int sched_clock_running;