DVDInterface: Reduce a global variable to translation unit scope

[lioncash]

g_bStream isn't used anywhere else.

Also corrects the prefixes on other translation unit scoped variables as well.

[JosJuice]

Reviewed 2 of 2 files at r1.
Review status: all files reviewed at latest revision, 1 unresolved discussion.

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Source/Core/Core/HW/DVDInterface.cpp, line 236 [r1] (raw file):
s_audio_position

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[JosJuice]

Reviewed 1 of 1 files at r2.
Review status: all files reviewed at latest revision, all discussions resolved.

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[degasus]

Reviewed 1 of 2 files at r1, 1 of 1 files at r2.
Review status: all files reviewed at latest revision, all discussions resolved, all commit checks successful.

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[BhaaLseN]

LGTM apart from those two underscores (which may or may not belong in this PR; but since you changed others it probably doesn't matter much...)

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Reviewed 1 of 2 files at r1, 1 of 1 files at r2.
Review status: all files reviewed at latest revision, 2 unresolved discussions, all commit checks successful.

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Source/Core/Core/HW/DVDInterface.cpp, line 509 [r2] (raw file):
You might want to rename this one too, while you're at it (underscore at start)

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Source/Core/Core/HW/DVDInterface.cpp, line 627 [r2] (raw file):
And perhaps this one too.

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[delroth]

Reviewed 1 of 2 files at r1, 1 of 1 files at r3.
Review status: all files reviewed at latest revision, 2 unresolved discussions.

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[delroth]

Reviewed 1 of 2 files at r1, 1 of 1 files at r3.
Review status: all files reviewed at latest revision, 2 unresolved discussions.

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[degasus]

Reviewed 1 of 1 files at r3.
Review status: all files reviewed at latest revision, 2 unresolved discussions.

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[JosJuice]

Reviewed 1 of 1 files at r3.
Review status: all files reviewed at latest revision, 2 unresolved discussions.

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