tigertool: fix regex
tigertool: fix regex

Change $ to \s in regex.

BUG=None (tigertail serserialno fail
TEST=./tigertool.py --setserialno test
BRANCH=none

Change-Id: I006ff8e70b3d20be44590c2050f9e341f10a2d53
Signed-off-by: Nick Sanders <f4566bb3c90c0bf5fa0906b296b1da45051a62ee@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2008450
Reviewed-by: YH Lin <a608809fda0b3a5e5ffc78f5b79106a21e96e6dd@chromium.org>
Reviewed-by: Aseda Aboagye <12c9b286316a940fd31c24070da5ab64cdd4d0e7@chromium.org>

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