fw-update: tests: add missing dependency
fw-update: tests: add missing dependency

The tests added with ef90b0d3b have an unlisted dependency on gmock,
which breaks the build when the gtest dependency is satisfied using the
suproject.  Add the missing dependency.

Change-Id: I352c8677c41d3763e252c92f590b1cbf68a5a612
Fixes: ef90b0d3b882766969afa2c2c430e1902bbc5e57
Signed-off-by: Brad Bishop <713d098c0be4c8fd2bf36a94cd08699466677ecd@fuzziesquirrel.com>

openbmc/pldm,openbmc/pldm,openbmc/pldm