Failure to terminate an of_device_id table can lead to confusing
failures depending on where the compiler places the array. Add a
check to make sure these tables are terminated. Thanks to Mitchel
Humpherys for coming up with the pattern initially.

Cc: Mitchel Humpherys <mitchelh@codeaurora.org>
Cc: Gilles Muller <Gilles.Muller@lip6.fr>
Cc: Nicolas Palix <nicolas.palix@imag.fr>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: devicetree@vger.kernel.org
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Acked-by: Grant Likely <grant.likely@linaro.org>
Signed-off-by: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Michal Marek <mmarek@suse.cz>