turbostat: Don't attempt to printf an off_t with %zx

turbostat uses the format %zx to print an off_t.  However, %zx wants a
size_t, not an off_t.  On 32-bit targets, those refer to different
types, potentially even with different sizes.  Use %llx and a cast
instead, since printf does not have a length modifier for off_t.

Without this patch, when compiling for a 32-bit target:

turbostat.c: In function 'get_msr':
turbostat.c:231:3: warning: format '%zx' expects argument of type 'size_t', but argument 4 has type 'off_t' [-Wformat]

Signed-off-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Len Brown <len.brown@intel.com>