build: update cereal dep for subprojects
build: update cereal dep for subprojects

Starting with meson 0.56, it seems preferable to use
'cmake.dependency' rather than 'cmake.get_variable' and with
meson 0.59, the 'get_variable' approach doesn't even work.
Update as appropriate.

Signed-off-by: Patrick Williams <cbb7353e6d953ef360baf960c122346276c6e320@stwcx.xyz>
Change-Id: I408e53082be6f8a3978acaa69072343796c36d8b

openbmc/phosphor-logging,openbmc/phosphor-logging,openbmc/phosphor-logging,openbmc/phosphor-logging