uvc compat XU ioctl fixes

uvc's compat XU ioctls go through tons of potentially buggy
indirection.  Patch 1 removes the indirection.  Patch 2 cleans up
the code.

Compile-tested only. I have the hardware, but I have absolutely no
idea what XU does, how to use it, what software to recompile as
32-bit, or what to test in that software.
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