nvmecontrol: Have to truncate on all 32-bit architectures

[imp]

Summary

armv7, powerpc, powerpcspe and i386 all lack 128-bit integer
types. Adjust the comment and #ifdef. I don't think we support nvme on
any of these other architectures at the moment, but it won't hurt to be
more precise.

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[jhb]

I used SIZEOF_LONG == 4 locally.

sbin/nvmecontrol/nvmecontrol.h

94

I fixed the i386 in this part of the comment as well.