ts: arib: use early return

It simplifies the handling of the different error cases, and ensure every case is ending with a return. The 3: case was not ending with a return before, leading to potential (harmless currently) fallthrough to the default case.

In addition, between one to two indentation level is saved, and the further the reader go through the function, the less guarantee there is to check before usage. For instance, after the beginning, p_dr is set to be valid without needing to check if we use it in the correct condition or not. Thus, even the error handling where breaks fall-through is simplified to just clean up existing objects.