Don't check for tank size information only on first tank

commit d681bdcb6308 ("Only use default cylinder for first one") has a
stupid bug in that it only calls get_tanksize for the first tank. That's
of course completely bogus.

Thanks to Linus for catching this.

Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>