btrfs: increment loop count outside critical section during metadata reclaim

btrfs: increment loop count outside critical section during metadata reclaim

In btrfs_preempt_reclaim_metadata_space() there's no need to increment the
local variable that tracks the number of iterations of the while loop
while inside the critical section delimited by the space_info's spinlock.
That spinlock is heavily used by space reservation and flushing code, so
it's desirable to have its critical sections as short as possible.
So move the loop count incremented outside the critical section.

Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>