btrfs: use scrub_pause_on/off() to reduce code in scrub_enumerate_chunks()

Use new intruduced scrub_pause_on/off() can make this code block
clean and more readable.

Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: Chris Mason <clm@fb.com>
1 file changed