startup: Fixed measure_clk to return kHz instead of MHz.

startup: Fixed measure_clk to return kHz instead of MHz.

The original code had iterated 10,000,000 times and taken the elapsed
time divided by 10,000, to yield kHz which is mathematically correct
only if we were measuring time in seconds, but we are measuring time in
 milliseconds, so the correct divisor is actually 10,000,000.  Previous
code would report 0.500 for actual measured speed of 500 kHz.

Change-Id: Iba4c4961fe3973e7ccfa6dfa11d606a966ceb50c
Signed-off-by: Ed Beroset <beroset@ieee.org>
Reviewed-on: http://openocd.zylin.com/2573
Tested-by: jenkins
Reviewed-by: Jens Bauer <jens@gpio.dk>
Reviewed-by: Paul Fertser <fercerpav@gmail.com>