util/ecst.c: Improve return values in calc_header_crc_bin
util/ecst.c: Improve return values in calc_header_crc_bin

Ensure consistency in types (TRUE/FALSE) and document the outcome in
the function header.

BUG=none
BRANCH=none
TEST=none

Change-Id: Ie3786f5de6f1a93813afd4a88be2994b690886c6
Signed-off-by: Patrick Georgi <bc411205f21846a74924ee7b489c75617ec76078@google.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/1793587
Reviewed-by: Daisuke Nojiri <fd5f93af191bf7e8f73ea71cc3c0f66b41b1dd49@chromium.org>
Tested-by: Patrick Georgi <bc411205f21846a74924ee7b489c75617ec76078@chromium.org>
Commit-Queue: Patrick Georgi <bc411205f21846a74924ee7b489c75617ec76078@chromium.org>

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