amdfwtool: Clear struct match before regular expression matching
If it is not cleared and the number of strings is fewer than last
iteration, the match[3] will keep the last value, which actually
should be empty.
Add assert to make sure the level is a legal value.
BUG=b:
222038278
Change-Id: If14e0923fbb1648d83784eb5dc1411c93227db5a
Signed-off-by: Zheng Bao <fishbaozi@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/62482
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>