btrfs: fix uninitialized return value in the ref-verify tool

In the ref-verify tool, when processing the inline references of an extent
item, we may end up returning with uninitialized return value, because:

1) The 'ret' variable is not initialized if there are no inline extent
   references ('ptr' == 'end' before the while loop starts);

2) If we find an extent owner inline reference we don't initialize 'ret'.

So fix these cases by initializing 'ret' to 0 when declaring the variable
and set it to -EINVAL if we find an extent owner inline references and
simple quotas are not enabled (as well as print an error message).

Reported-by: Mirsad Todorovac <mtodorovac69@gmail.com>
Link: https://lore.kernel.org/linux-btrfs/59b40ebe-c824-457d-8b24-0bbca69d472b@gmail.com/
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

Author: fdmanana

fs/btrfs/ref-verify.c

@@ -441,7 +441,8 @@ static int process_extent_item(struct btrfs_fs_info *fs_info,
 	u32 item_size = btrfs_item_size(leaf, slot);
 	unsigned long end, ptr;
 	u64 offset, flags, count;
-	int type, ret;
+	int type;
+	int ret = 0;
 
 	ei = btrfs_item_ptr(leaf, slot, struct btrfs_extent_item);
 	flags = btrfs_extent_flags(leaf, ei);
@@ -486,7 +487,11 @@ static int process_extent_item(struct btrfs_fs_info *fs_info,
 						  key->objectid, key->offset);
 			break;
 		case BTRFS_EXTENT_OWNER_REF_KEY:
-			WARN_ON(!btrfs_fs_incompat(fs_info, SIMPLE_QUOTA));
+			if (!btrfs_fs_incompat(fs_info, SIMPLE_QUOTA)) {
+				btrfs_err(fs_info,
+			  "found extent owner ref without simple quotas enabled");
+				ret = -EINVAL;
+			}
 			break;
 		default:
 			btrfs_err(fs_info, "invalid key type in iref");