btrfs: do proper error handling in btrfs_update_reloc_root

btrfs: do proper error handling in btrfs_update_reloc_root

BugLink: https://bugs.launchpad.net/bugs/1928857
[ Upstream commit 592fbcd50c99b8adf999a2a54f9245caff333139 ]

We call btrfs_update_root in btrfs_update_reloc_root, which can fail for
all sorts of reasons, including IO errors.  Instead of panicing the box
lets return the error, now that all callers properly handle those
errors.

Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>