btrfs: use a single if() statement for one outcome in get_block_rsv()

Rather than have three separate if() statements for the same outcome
we should just OR them together in the same if() statement.
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NAlexandru Moise <00moses.alexander00@gmail.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

fs/btrfs/extent-tree.c

@@ -4891,13 +4891,9 @@ static struct btrfs_block_rsv *get_block_rsv(
 {
 	struct btrfs_block_rsv *block_rsv = NULL;
 
-	if (test_bit(BTRFS_ROOT_REF_COWS, &root->state))
-		block_rsv = trans->block_rsv;
-
-	if (root == root->fs_info->csum_root && trans->adding_csums)
-		block_rsv = trans->block_rsv;
-
-	if (root == root->fs_info->uuid_root)
+	if (test_bit(BTRFS_ROOT_REF_COWS, &root->state) ||
+	    (root == root->fs_info->csum_root && trans->adding_csums) ||
+	     (root == root->fs_info->uuid_root))
 		block_rsv = trans->block_rsv;
 
 	if (!block_rsv)