btrfs: qgroup: set quota enabled bit if quota disable fails flushing reservations

Before waiting for the rescan worker to finish and flushing reservations,
we clear the BTRFS_FS_QUOTA_ENABLED flag from fs_info. If we fail flushing
reservations we leave with the flag not set which is not correct since
quotas are still enabled - we must set back the flag on error paths, such
as when we fail to start a transaction, except for error paths that abort
a transaction. The reservation flushing happens very early before we do
any operation that actually disables quotas and before we start a
transaction, so set back BTRFS_FS_QUOTA_ENABLED if it fails.

Fixes: af0e2aab ("btrfs: qgroup: flush reservations during quota disable")
CC: stable@vger.kernel.org # 6.12+
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>