Why rename at all? It's pretty obvious it's a reference count. Count/counter is not an unusual name to use for a reference count, it even has get and put helpers...
I understand as the member count is in btrfs_block_group so prefix bg_ looks redundant, but prefix bg_ is still useful. With out the prefix, the grep ">count" *.c didn't help straight away to verify where is block_group count used. At two places we missed using the get helper which the patch 3/3 fixed.
It's ok to drop this rename patch if you find it's not inline with the rest of the codes.
