btrfs-progs: check: fix extents after finding all errors

btrfs-progs: check: fix extents after finding all errors

Simplifying the logic of fixing.

Calling fixup_extent_ref() after encountering every error causes
more error messages after the extent is fixed. In case of multiple errors,
this is confusing because the error message is displayed after the fix
message and it works on stale data. It is best to show all errors and
then fix the extents.

Set a variable and call fixup_extent_ref() if it is set. err is not used,
so cleared it.

Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>