CEC: Validate <Vendor Command> correctly

The command always has one or more bytes for its parameter, so
the right validation should have been the one ensuring the number
of bytes (1 ~ 14).

Bug: 24986703
Change-Id: I171e971f1649761d69ffe2aa0af364f34dc9ac3e
(cherry picked from commit 4808581f4dfdf04adcd2646e152dede0ce418cad)