UPSTREAM: zram: clear disk io accounting when reset zram device

(cherry-pick from commit d7ad41a1c498729b7584c257710b1b437a0c1470)

Clear zram disk io accounting when resetting the zram device.  Otherwise
the residual io accounting stat will affect the diskstat in the next
zram active cycle.

Bug: 25951511

Change-Id: I426e4c70d31393aa9a9ee3c9984e029ceb6f756b
Signed-off-by: Weijie Yang <weijie.yang@samsung.com>
Acked-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>