target: Fix snprintf format string and argument mismatch in md output

Commit 47b8cf84 changed the fixed type of the value argument to snprint
but didn't change the format string to match for sizes != 64 bit.

Change-Id: I908b06f49ab69d04224282949190a0de883048e0
Signed-off-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>
Reviewed-on: http://openocd.zylin.com/4167


Tested-by: jenkins
Reviewed-by: Stian Skjelstad <stian@nixia.no>
Reviewed-by: Philipp Guehring <pg@futureware.at>