util/tagbranch: Update for COIL
util/tagbranch: Update for COIL

The primary branch name has changed, so update the script to reflect
that.

BRANCH=none
BUG=b:163885307
TEST=none

Signed-off-by: Tom Hughes <fc5c12f30a5ed2baa0581f44ee14ad1eb7b20d83@chromium.org>
Change-Id: I16cc9770d3e6d92adace1f527bb5d31eaa3506f2
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3298871
Reviewed-by: Daisuke Nojiri <fd5f93af191bf7e8f73ea71cc3c0f66b41b1dd49@chromium.org>

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