btrfs: remove unnecessary -ERANGE check in btrfs_get_acl

There is no chance to get into -ERANGE error condition because we first
call btrfs_getxattr to get the length of the attribute, then we do a
subsequent call with the size from the first call.  Between the 2 calls
the size shouldn't change. So remove the unnecessary -ERANGE error
check.

Signed-off-by: Chengguang Xu <cgxu519@gmx.com>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>