btrfs: fix uninitialized variable warning in btrfs_update_block_group

[ Upstream commit efbf35a1 ]

reclaim isn't set in the alloc case, however we only care about
reclaim in the !alloc case.  This isn't an actual problem, however
-Wmaybe-uninitialized will complain, so initialize reclaim to quiet the
compiler.

Reviewed-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Stable-dep-of: df384da5 ("btrfs: use temporary variable for space_info in btrfs_update_block_group")
Signed-off-by: Sasha Levin <sashal@kernel.org>