strmhz: Make hz unsigned to support greater than 2146 MHz clock

For example, an input of 0x80000000 should print:

2147.484 instead of -2147.-483.

Signed-off-by: Ed Swarthout <Ed.Swarthout@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>