s3: report errors on bucket creation (mkdir) correctly

Before this fix errors on bucket creation were being silently
swallowed.

See: https://forum.rclone.org/t/rclone-with-brand-new-aws-account-for-s3/15590

backend/s3/s3.go

@@ -1738,7 +1738,7 @@ func (f *Fs) makeBucket(ctx context.Context, bucket string) error {
 				err = nil
 			}
 		}
-		return nil
+		return err
 	}, func() (bool, error) {
 		return f.bucketExists(ctx, bucket)
 	})