disable new gcc-7.1.1 warnings for now

I made the mistake of upgrading my desktop to the new Fedora 26 that
comes with gcc-7.1.1.

There's nothing wrong per se that I've noticed, but I now have 1500
lines of warnings, mostly from the new format-truncation warning
triggering all over the tree.

We use 'snprintf()' and friends in a lot of places, and often know that
the numbers are fairly small (ie a controller index or similar), but gcc
doesn't know that, and sees an 'int', and thinks that it could be some
huge number.  And then complains when our buffers are not able to fit
the name for the ten millionth controller.

These warnings aren't necessarily bad per se, and we probably want to
look through them subsystem by subsystem, but at least during the merge
window they just mean that I can't even see if somebody is introducing
any *real* problems when I pull.

So warnings disabled for now.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>