Qt/GCMemcardCreateNewDialog: Use zero values for formatting instead of accessing g_SRAM.

[AdmiralCurtiss]

GUI code should not be directly accessing emulated hardware like this.

As for the CardFlashId value itself... frankly, I don't believe the value itself actually matters in the slightest. I've checked various dumped memory cards of mine and it looks like a completely random set of 12 bytes to me for them, while all my Dolphin-generated cards use either 12 zeros like what I'm using in this PR (which happens when you create a card before launching a game, as g_SRAM is zero-filled before first boot), or the ASCII DOLPHINSLOTA as seen here. Gamecube software does not seem to care what it is -- it probably just matters that the serial in the header is correctly synced with the flash ID, which we ensure here when mounting a card and here when formatting a card.

As a sidenote... am I right in assuming that this flash ID on real hardware is a separate piece of information provided by a memory card, disconnected from formatted header data? Cause we emulate it by just assuming the header block is always correct. Which is probably fine, but just wondering.

[AdmiralCurtiss]

Oh, alternatively, we could also just generate a random flash ID instead. Would that be preferable?

[leoetlino]

All those values are already zero on master when you create a card prior to launching a game, so I think this change is fine.