flash_ec: Look for npcx_monitor.bin in the same dir as ec.bin
flash_ec: Look for npcx_monitor.bin in the same dir as ec.bin

crrev.com/1194646 makes it so chromeos-ec installs the monitor.bin as
part of the build. The script just needs to be updated to use it. This
will allow using flash_ec for downloaded firmware or firmware built
using emerge chromeos-ec.

BUG=b:113288489
BRANCH=none
TEST=emerge-grunt chromeos-ec && flash_ec --board=grunt

Change-Id: Ie92b75a750dbf8ce4e01eafec7a01479915b1270
Signed-off-by: Raul E Rangel <9a9c998e11a2655b1de9a05eeeef5f710c0dc7ed@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1194354
Reviewed-by: Jett Rink <9d4aef0593e6843318d99df31597fb6153b89787@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec