Remove err nil check

since type checking nil will not panic and return appropriately

Signed-off-by: Manish Tomar <manish.tomar@docker.com>

registry/storage/garbagecollect.go

@@ -98,15 +98,13 @@ func MarkAndSweep(ctx context.Context, storageDriver driver.StorageDriver, regis
 			return nil
 		})
-		if err != nil {
-			// In certain situations such as unfinished uploads, deleting all
-			// tags in S3 or removing the _manifests folder manually, this
-			// error may be of type PathNotFound.
-			//
-			// In these cases we can continue marking other manifests safely.
-			if _, ok := err.(driver.PathNotFoundError); ok {
-				return nil
-			}
+		// In certain situations such as unfinished uploads, deleting all
+		// tags in S3 or removing the _manifests folder manually, this
+		// error may be of type PathNotFound.
+		//
+		// In these cases we can continue marking other manifests safely.
+		if _, ok := err.(driver.PathNotFoundError); ok {
+			return nil
 		}
 		return err