btrfs: always update fstrim_range on failure in FITRIM ioctl

Even in case of failure we could've discarded some data and userspace
should be made aware of it, so copy fstrim_range to userspace
regardless.

Also make sure to update the trimmed bytes amount even if
btrfs_trim_free_extents fails.

CC: stable@vger.kernel.org # 5.15+
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Luca Stefani <luca.stefani.ge1@gmail.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>