FROMGIT: f2fs: fix iostat related lock protection

Made iostat related locks safe to be called from irq context again.

Cc: <stable@vger.kernel.org>
Fixes: a1e09b03 ("f2fs: use iomap for direct I/O")
Signed-off-by: Daeho Jeong <daehojeong@google.com>
Reviewed-by: Stanley Chu <stanley.chu@mediatek.com>
Tested-by: Eddie Huang <eddie.huang@mediatek.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
(cherry picked from commit f8ed39ad779fbc5d37d08e83643384fc06e4bae4 git://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs.git dev)
Change-Id: I76cdcb88e686fbd9e1847de57eb9f8f25034f59b