timeconst.pl: correct reversal of USEC_TO_HZ and HZ_TO_USEC

The USEC_TO_HZ and HZ_TO_USEC constant sets were mislabelled, with
seriously incorrect results.  This among other things manifested
itself as cpufreq not working when a tickless kernel was configured.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Tested-by: Carlos R. Mafra <crmafra@ift.unesp.br>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>