faft: Use super-class FAFTSequence setup for EC write-protection setting

FAFTSequence supports EC write-protection setup. Use it instead of doing
the same thing in the test.

BUG=chrome-os-partner:15835
TEST=run_remote_tests --board link --remote dut ECWriteProtect/control$

Change-Id: Ib1931b70706df73085f8cf10a69d7e32282e525a
Reviewed-on: https://gerrit.chromium.org/gerrit/38642
Reviewed-by: Vic Yang <victoryang@chromium.org>
Commit-Ready: Tom Wai-Hong Tam <waihong@chromium.org>
Tested-by: Tom Wai-Hong Tam <waihong@chromium.org>
1 file changed