cxl: avoid returning uninitialized error code

The new cxl_add_to_region() function returns an uninitialized
value on success:

drivers/cxl/core/region.c:2628:6: error: variable 'rc' is used uninitialized whenever 'if' condition is false [-Werror,-Wsometimes-uninitialized]
        if (IS_ERR(cxlr)) {
            ^~~~~~~~~~~~
drivers/cxl/core/region.c:2654:9: note: uninitialized use occurs here
        return rc;

Simplify the logic to have the rc variable always initialized in the
same place.

Fixes: a32320b ("cxl/region: Add region autodiscovery")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20230213101220.3821689-1-arnd@kernel.org
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

Author: arndb

drivers/cxl/core/region.c

@@ -2623,10 +2623,9 @@ int cxl_add_to_region(struct cxl_port *root, struct cxl_endpoint_decoder *cxled)
 		cxlr = to_cxl_region(region_dev);
 	mutex_unlock(&cxlrd->range_lock);
 
-	if (IS_ERR(cxlr)) {
-		rc = PTR_ERR(cxlr);
+	rc = PTR_ERR_OR_ZERO(cxlr);
+	if (rc)
 		goto out;
-	}
 
 	attach_target(cxlr, cxled, -1, TASK_UNINTERRUPTIBLE);