i2c_probe: update for use in scripting

Allow the use of an I2C address to test and return success
if one or more devices is found.

This allows device presence to alter the flow of a script.
e.g.
   if i2c probe 0x04 ; then
	echo found Hannstar touch ;
   fi

Signed-off-by: Eric Nelson <eric.nelson@boundarydevices.com>