btrfs: Fix 64 bit divide problem
This fixes a regression introduced by
cdcb725c05fe0cb71777c66ddc2445fedbbb3c59
In cases where we need to divide/multiply by 2 we should just
left/right shift respectively, and in cases where theres N
number of devices use do_div. Also make the counters u64 to
match up with rw_devices.
Signed-off-by: Josef Bacik <josef@redhat.com>
Cc: torvalds@linux-foundation.org
Cc: liubo2009@cn.fujitsu.com
Link: http://lkml.kernel.org/r/1313843391-3904-1-git-send-email-josef@redhat.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>