btrfs: drop NOFAIL from set_extent_bit allocation masks

The __GFP_NOFAIL passed to set_extent_bit first appeared in 2010
(commit f0486c68 ("Btrfs: Introduce contexts for metadata
reservation")), without any explanation why it would be needed.

Meanwhile we've updated the semantics of set_extent_bit to handle failed
allocations and do unlock, sleep and retry if needed.  The use of the
NOFAIL flag is also an outlier, we never want any of the set/clear
extent bit helpers to fail, they're used for many critical changes like
extent locking, besides the extent state bit changes.
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/block-group.c

@@ -3523,8 +3523,7 @@ int btrfs_update_block_group(struct btrfs_trans_handle *trans,
 
 			set_extent_bit(&trans->transaction->pinned_extents,
 				       bytenr, bytenr + num_bytes - 1,
-				       EXTENT_DIRTY, NULL,
-				       GFP_NOFS | __GFP_NOFAIL);
+				       EXTENT_DIRTY, NULL, GFP_NOFS);
 		}
 
 		spin_lock(&trans->transaction->dirty_bgs_lock);

fs/btrfs/extent-tree.c

@@ -2508,8 +2508,7 @@ static int pin_down_extent(struct btrfs_trans_handle *trans,
 	spin_unlock(&cache->space_info->lock);
 
 	set_extent_bit(&trans->transaction->pinned_extents, bytenr,
-		       bytenr + num_bytes - 1, EXTENT_DIRTY, NULL,
-		       GFP_NOFS | __GFP_NOFAIL);
+		       bytenr + num_bytes - 1, EXTENT_DIRTY, NULL, GFP_NOFS);
 	return 0;
 }