cxl/region: Cleanup target list on attach error

Jonathan noticed that the target list setup is not unwound completely
upon error. Undo all the setup in the 'err_decrement:' exit path.

Fixes: 27b3f8d138 ("cxl/region: Program target lists")
Reported-by: Jonathan Cameron <Jonathan.Cameron@Huawei.com>
Link: http://lore.kernel.org/r/20230208123031.00006990@Huawei.com
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Vishal Verma <vishal.l.verma@intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: https://lore.kernel.org/r/167601996980.1924368.390423634911157277.stgit@dwillia2-xfh.jf.intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/cxl/core/region.c

@@ -1347,6 +1347,8 @@ static int cxl_region_attach(struct cxl_region *cxlr,
 
 err_decrement:
 	p->nr_targets--;
+	cxled->pos = -1;
+	p->targets[pos] = NULL;
 err:
 	for (iter = ep_port; !is_cxl_root(iter);
 	     iter = to_cxl_port(iter->dev.parent))