Fix an issue with asynchronous execution in `dpnp.fft` module

[vtavana]

In this PR, an issue regarding asynchronous execution of dpnp.fft module is resolved. In the process of padding the input arrays, dependent event list (dep_evs) was obtained before creating the new zero array which by itself add a new dependent event to dep_evs list. So, we need to get dep_evs after calling dpnp.zeros.

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