You need to be comparing the result of GetCheckoutStatus to one of the CheckoutStatus enumerations:
OwnedByCurrentUser - The element is owned by the current user.
OwnedByOtherUser - The element is owned by some user other than the current user.
NotOwned - The element is not owned by any user.
For example:
if (WorksharingUtils.GetCheckoutStatus(doc, view.Id) != CheckoutStatus.NotOwned)
Additionally, note that I removed the cast to Element - it is not required here.