Makefile: Add missing semicolon after 'unsupported' message

Make it bail out instead of printing "exit 1".

Change-Id: I58c00eb7faa661351b1f00e477f0e8ccc08854a3
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/c/flashrom-stable/+/73444
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
1 file changed